From: "Richard Krehbiel" Newsgroups: comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.soundcard.advocacy,comp.sys.ibm.pc.soundcard.tech,comp.sys.ibm.pc.hardware.chips,alt.folklore.computers Subject: Computers without interrupts or DMA Date: Fri, 9 Oct 1998 12:14:14 -0400 Organization: Kastle Systems Lines: 23 Message-ID: <6vlcoo$d8r@agora.dmz.khoral.com> References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> NNTP-Posting-Host: charon.dmz.khoral.com X-Newsreader: Microsoft Outlook Express 4.72.3115.0 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3110.3 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.belnet.be!news-raspail.gip.net!news-peer.gip.net!news.gsl.net!gip.net!news.idt.net!nntp2.cerf.net!socal.verio.net!nntp.ni.net!agora.dmz.khoral.com!usenet Werner wrote in message <36441857.365679098@gateway.axioma.co.at>... >Mikka wrote: > >> >>Or you could get a Mac, which doesn't use IRQs. That's not a "PC" >>either. >In fact every computer uses interrupts (and DMAs), the Mac only is >able to shield the user from these nasty things. Actually, my old TRS-80 Model I (1977) had no interrupts. The very first instruction executed by the system ROM at startup was "DI" (Disable Interrupts) and they were never re-enabled. It did have one DMA-ish circuit which performed video refresh. The Sinclair ZX-80 didn't even have video refresh DMA; it used the Z80 CPU to move bytes from video RAM to the display circuit. I don't know whether it had any interrupts. -- Richard Krehbiel, Kastle Systems, Arlington VA USA rich@kastle.com (work) or richk@mnsinc.com (personal) ###### Path: chonsp.franklin.ch!usenet From: Neil Franklin Newsgroups: comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.soundcard.advocacy, comp.sys.ibm.pc.soundcard.tech,comp.sys.ibm.pc.hardware.chips,alt.folklore.compu ters Subject: Re: Computers without interrupts or DMA Date: 09 Oct 1998 23:50:33 +0200 Organization: My own Private Self Lines: 47 Message-ID: References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> X-Newsreader: Gnus v5.3/Emacs 19.34 "Richard Krehbiel" writes: > > Actually, my old TRS-80 Model I (1977) had no interrupts. The very first > instruction executed by the system ROM at startup was "DI" (Disable > Interrupts) and they were never re-enabled. ROM waster. The Z80 CPU started up with interrupts disabled. You had to EI (after setting up an handler) to use them. As I once wrote standallone (no OS) Z80 code, I know this. Hey, I lerned programming on one of them. > It did have one DMA-ish circuit > which performed video refresh. Like nearly all computers with video output. > The Sinclair ZX-80 didn't even have video refresh DMA; it used the Z80 CPU > to move bytes from video RAM to the display circuit. Anyone know how they managed this on an 2.5MHz Z80? I know the Xerox Alto did this. But that was an 5.94MHz 16bit system and it had to do it in the microcode to be fast enough (it still cost 2/3 of CPU power). Also the Xerox used bitmapped video, which the ZX80 with its 1kByte RAM could not do. So you have additional character lookup time. Actually I suspect this story to be not true. The ZX81 used DMA hardware for outputting the pixels and software to generate the line sync signals. Anyone got the ZX80/ZX81 code and/or schematics? > I don't know whether it had any interrupts. The ZX80 and ZX81 expansion port was simply a full copy of the Z80 CPU pins. So /INT would be there. Whether the BASIC made use of them is annother question. -- *** New home Addresses Mail and Web *** home: neil@franklin.ch.remove http://neil.franklin.ch/ work: franklin@arch.ethz.ch.remove http://caad.arch.ethz.ch/~franklin/ Microsoft is Software Communism, Fight for GNU Freedom! ###### From: Marcin Nowak Newsgroups: comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.soundcard.advocacy,comp.sys.ibm.pc.soundcard.tech,comp.sys.ibm.pc.hardware.chips,alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: 13 Oct 1998 16:31:37 +0200 Organization: CERN - European Laboratory for Particle Physics Lines: 7 Message-ID: References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> NNTP-Posting-Host: pcitasd15.cern.ch X-Trace: sunnews.cern.ch 908289096 15856 (None) 137.138.38.15 X-Complaints-To: news@sunnews.cern.ch X-Newsreader: Gnus v5.3/Emacs 19.34 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!cern.ch!news "Richard Krehbiel" writes: > The Sinclair ZX-80 didn't even have video refresh DMA; it used the Z80 CPU > to move bytes from video RAM to the display circuit. I don't know whether > it had any interrupts. Sure it had. Something had to trigger the display refresh. Marcin ###### From: jmfbahciv@aol.com Newsgroups: alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: Wed, 14 Oct 98 09:50:36 GMT Organization: UltraNet Communications, Inc. Lines: 18 Message-ID: <7020ga$qrm$1@strato.ultra.net> References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> NNTP-Posting-Host: d14.dial-11.mbo.ma.ultra.net X-Complaints-To: abuse@ultra.net X-Ultra-Time: 14 Oct 1998 11:04:42 GMT X-Newsreader: News Xpress Version 1.0 Beta #4 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.belnet.be!newspump.monmouth.com!newspeer.monmouth.com!news.ultranet.com!d14 [I snipped all those newsgroups] In article , Marcin Nowak wrote: >"Richard Krehbiel" writes: >> The Sinclair ZX-80 didn't even have video refresh DMA; >>it used the Z80 CPU to move bytes from video RAM to the >>display circuit. I don't know whether it had any interrupts. > > Sure it had. Something had to trigger the display refresh. > Marcin This begs the question: Are computers without interrupts interesting? And, if they are, how are/were they used? /BAH Sigh! - Subtract a hundred and four for e-mail. ###### From: "George R. Gonzalez" Newsgroups: alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: Wed, 14 Oct 1998 10:41:27 -0500 Organization: SkyPoint Communications, Inc. Lines: 29 Message-ID: <702gug$4iq$1@shadow.skypoint.net> References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <7020ga$qrm$1@strato.ultra.net> <3624C21E.5A2E@gazonk.del> NNTP-Posting-Host: dial051.skypoint.net Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit X-Newsreader: Microsoft Outlook Express 4.72.3110.5 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3110.3 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!news.maxwell.syr.edu!newsfeed.cwix.com!199.170.121.3!falcon.america.net!news.pagesat.net!skypoint.com!not-for-mail Foobar T. Clown wrote in message <3624C21E.5A2E@gazonk.del>... >jmfbahciv@aol.com wrote: >> >> Are computers without interrupts interesting? And, if they are, >> how are/were they used? If your computer is complex, interrupts can be very hard to handle. When an interrupt occurs, it has to be possible to save the complete machine state, and restore it after the interrupt. In a simple machine, saving the state is no big deal-- just save a few registers. But what about a really complex CPU, with multiple functional units, pipelining, instruction pre-fetch...? The machine state becomes very complex, requiring many bytes to be pushed onto the stack. Then there's the case where the designer made a mistake, and some important bit of machine state isnt saveable. This happened with the CDC Star, and they had to manually redesign a considerable portion of the CPU to make the state saveable. Also if you have a complex and expensive CPU, do you really want it to be handling every trivial keyboard interrupt? You might opt to forget about interrupts and have some other cheaper processor handle all the I/O. This is the way the CDC 6000 series went. ###### Message-ID: <3624C21E.5A2E@gazonk.del> Date: Wed, 14 Oct 1998 11:24:14 -0400 From: "Foobar T. Clown" Reply-To: foobar@gazonk.del Organization: Blurp X-Mailer: Mozilla 3.01 (WinNT; I) MIME-Version: 1.0 Newsgroups: alt.folklore.computers Subject: Re: Computers without interrupts or DMA References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <7020ga$qrm$1@strato.ultra.net> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit NNTP-Posting-Host: 198.133.110.49 X-Trace: 14 Oct 1998 11:24:23 -0500, 198.133.110.49 Lines: 26 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.belnet.be!212.63.192.161.MISMATCH!newshub.bart.net!news.tele2.nl!newsfeed1.swip.net!swipnet!howland.erols.net!ix.netcom.com!zeus.nomos.com!198.133.110.49 jmfbahciv@aol.com wrote: > > Are computers without interrupts interesting? And, if they are, > how are/were they used? I used to program on engineering workstations with bit-mapped displays, GUIs, mice, preemptive multi-tasking, and demand paged, protected, virtual memory, but no interrupts... ...Well, no interrupt HARDWARE, anyway. They were PERQs, made by Three Rivers Computer, Inc., in Pittsburgh PA. The CPU was a clean, simple microcode engine with a writeable control store. We ran microcode emulators for a UCSD-P-System-like instruction set and, for a custom LISP instruction set. The only sense in which there were interrupts was that both emulators would poll for certain external conditions after completing each instruction, and would appropriately alter the virtual machine context if an event occurred. When you wrote microcode for a PERQ, you had to be careful to poll the vertical retrace bit often enough, and call a special microcode subroutine when it was set, otherwise you'd loose the video signal. So how did it do I/O? Like any *REAL* computer, it had a separate I/O processor and a separate network processor to take care of the ugly, bit pushing. ###### Message-ID: <3624C54B.3647@gazonk.del> Date: Wed, 14 Oct 1998 11:37:47 -0400 From: "Foobar T. Clown" Reply-To: foobar@gazonk.del Organization: Blurp X-Mailer: Mozilla 3.01 (WinNT; I) MIME-Version: 1.0 Newsgroups: alt.folklore.computers Subject: Re: Computers without interrupts or DMA References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <7020ga$qrm$1@strato.ultra.net> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit NNTP-Posting-Host: 198.133.110.49 X-Trace: 14 Oct 1998 11:37:56 -0500, 198.133.110.49 Lines: 19 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!news.maxwell.syr.edu!ix.netcom.com!zeus.nomos.com!198.133.110.49 jmfbahciv@aol.com wrote: > > Are computers without interrupts interesting? And, if they are, > how are/were they used? Is a PIC a computer? Low-end PICs don't have interrupts. They are used for things like making a car's turn signals blink, and interfacing keypads, sensors, and etc. to serial ports. Not only does a PIC not have a serial port interrupt... It doesn't even have a UART. You have to process a serial bit stream one bit at a time from a software timing loop. I've written softare for bare-metal, embedded applications where the processor and hardware had interrupt capability, but I chose to leave it disabled. Sometimes, when polling works, using ISRs just makes the software harder to understand and maintain. Maybe these are not the kinds of applications you were thinking of when you said, "computers." ###### Message-ID: <3624B05B.59F5F0CF@trailing-edge.com> From: Tim Shoppa Organization: Trailing Edge Technology X-Mailer: Mozilla 3.03Gold (X11; I; OpenVMS V7.0 DEC 3000 Model 300L) MIME-Version: 1.0 Newsgroups: comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.soundcard.advocacy,comp.sys.ibm.pc.soundcard.tech,comp.sys.ibm.pc.hardware.chips,alt.folklore.computers Subject: Re: Computers without interrupts or DMA References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 17 Date: Wed, 14 Oct 1998 14:08:27 -0400 NNTP-Posting-Host: 198.232.144.27 X-Trace: audrey2.cais.com 908388982 198.232.144.27 (Wed, 14 Oct 1998 14:16:22 EDT) NNTP-Posting-Date: Wed, 14 Oct 1998 14:16:22 EDT Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!isdnet!uu.fr!outfeed1.news.cais.net!in1.nntp.cais.net!199.0.216.204.MISMATCH!audrey2.cais.com!not-for-mail Marcin Nowak wrote: > > "Richard Krehbiel" writes: > > The Sinclair ZX-80 didn't even have video refresh DMA; it used the Z80 CPU > > to move bytes from video RAM to the display circuit. I don't know whether > > it had any interrupts. > > Sure it had. Something had to trigger the display refresh. You're mistakenly assuming that the ZX-80 can do a display refresh while running user programs; you'll probably be surprised when I tell you it can't! While doing the display refresh, the ZX-80 does nothing more than scan the keyboard for keypresses. And while a user program (as opposed to the wait-for-keypress loop) is running, the screen is completely blank. Tim. ###### From: Tom E Arnold Newsgroups: comp.sys.ibm.pc.hardware.systems,alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: Wed, 14 Oct 1998 21:09:48 -0500 Organization: Born to Raise Eyebrows Lines: 33 Message-ID: <703l9j$89g@newsops.execpc.com> References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <3624B05B.59F5F0CF@trailing-edge.com> Reply-To: tomea@execpc.com NNTP-Posting-Host: alzarius-1-104.mdm.mke.execpc.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Trace: daily-planet.newsops.execpc.com 908417139 8496 (None) 169.207.129.104 X-Complaints-To: abuse@execpc.com X-Mailer: Mozilla 3.03Gold (Win95; I) Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!nntprelay.mathworks.com!europa.clark.net!169.207.30.81!newsfeeds.sol.net!newsops.execpc.com!posts.execpc.com!daily-planet.newsops.execpc.com!usenet Tim Shoppa wrote: > > Marcin Nowak wrote: > > > > "Richard Krehbiel" writes: > > > The Sinclair ZX-80 didn't even have video refresh DMA; it used the Z80 CPU > > > to move bytes from video RAM to the display circuit. I don't know whether > > > it had any interrupts. > > > > Sure it had. Something had to trigger the display refresh. > > You're mistakenly assuming that the ZX-80 can do a display refresh > while running user programs; you'll probably be surprised when I > tell you it can't! While doing the display refresh, the ZX-80 > does nothing more than scan the keyboard for keypresses. And > while a user program (as opposed to the wait-for-keypress loop) > is running, the screen is completely blank. > The ZX-81, whowever, did have a display refresh, and it was interrupt driven. IIRC, the interrupt circuitry pulled a 60 Hz edge out of the power supply. The wait for keypress loop also debounced the awful keyboard, by looking for more keypress. I installed a fullsize keyboard, using an old Microswitch keypunch rig with _mechanical_ debounce, and the durn thing couldna see it. I built a MicroAce (Sinclair clone) from a kit, and at one time understood what every gate in the thing did. Thats the advantage of a crude little system. -- TEA/ My current neighborhood: http://www.coldspringpark.org My next neighborhood: http://www.geocities.com/athens/acropolis/9361 ###### From: "Rick Lugg" Newsgroups: alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: Thu, 15 Oct 1998 09:23:56 +0200 Organization: The South African Internet Exchange Lines: 33 Message-ID: <70484i$sf6$1@news2.saix.net> References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com><3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net><361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at><6vlcoo$d8r@agora.dmz.khoral.com> <7020ga$qrm$1@strato.ultra.net> NNTP-Posting-Host: qit-prxy-0000.telkom.co.za X-Newsreader: Microsoft Outlook Express 4.72.3110.5 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.3110.3 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!news.maxwell.syr.edu!netnews.com!news.idt.net!newsfeed.axxsys.net!router1.news.adelphia.net!uunet!in1.uu.net!news2.saix.net!not-for-mail Even though the early 60's commercial systems may have had interrupts, iirc they were not always made use of. I seem to recall that in the NCR 315 after issuing a line for printing, the OS used to loop checking the printer status register for completion. I just think that in the absence of formal multiprogramming OS, that approach didn't seem too silly at the time. A relatively simple change, permitted a background print despooler to "simultaneously" extract from a CRAM (yes!) and print, whilst the other programs happily did their thing. Rick Lugg jmfbahciv@aol.com wrote in message <7020ga$qrm$1@strato.ultra.net>... >[I snipped all those newsgroups] > >In article , > Marcin Nowak wrote: >>"Richard Krehbiel" writes: >>> The Sinclair ZX-80 didn't even have video refresh DMA; >>>it used the Z80 CPU to move bytes from video RAM to the >>>display circuit. I don't know whether it had any interrupts. >> >> Sure it had. Something had to trigger the display refresh. >> Marcin > >This begs the question: Are computers without interrupts >interesting? And, if they are, how are/were they used? > >/BAH > >Sigh! - Subtract a hundred and four for e-mail. ###### From: dg@ (David Given) Newsgroups: comp.sys.ibm.pc.hardware.systems,alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: Thu, 15 Oct 1998 12:36:20 GMT Organization: I'm organised? Wow! Message-ID: <908454980.293.0.nnrp-10.9e9878e0@news.demon.co.uk> References: <3624B05B.59F5F0CF@trailing-edge.com> <703l9j$89g@newsops.execpc.com> NNTP-Posting-Host: taos.demon.co.uk X-NNTP-Posting-Host: taos.demon.co.uk:158.152.120.224 X-Trace: news.demon.co.uk 908454980 nnrp-10:293 NO-IDENT taos.demon.co.uk:158.152.120.224 X-Complaints-To: abuse@demon.net Lines: 28 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.belnet.be!newsfeed.wirehub.nl!btnet-peer!btnet!dispose.news.demon.net!demon!news.demon.co.uk!demon!taos.demon.co.uk!!dg In article <703l9j$89g@newsops.execpc.com>, Tom E Arnold wrote: [...] >I built a MicroAce (Sinclair clone) from a kit, and at one time >understood what every gate in the thing did. Thats the advantage of a >crude little system. I wonder... These days, you can buy embedded Z80 controllers-on-a-chip. They look like fat EPROMS. They contain a processor, I/O ports, RAM, EPROM, and most of the necessary glue circuitry to make it all work. All you need, IIRC, is a clock circuit, which can be either a crystal or an RC oscillator. Would it be possible to make a ZX81 or Spectrum clone from one of these? All the hard stuff has already been done (not that ZX81's are very complex). You'd need to fake up the custom chips somehow. Possibly PLA's or FPGA's would help here. The controller's memory map might be awkward, and it might not export the full bus. It could make quite a nice little project. -- +- David Given ----------------+ | Work: dg@tao.co.uk | Smash the state, and have a nice day. | Play: dgiven@iname.com | +- http://wiredsoc.ml.org/~dg -+ ###### From: jmfbahciv@aol.com Newsgroups: alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: Thu, 15 Oct 98 12:45:25 GMT Organization: UltraNet Communications, Inc. Lines: 36 Message-ID: <704v4c$k2u$4@strato.ultra.net> References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <3624C21E.5A2E@gazonk.del> NNTP-Posting-Host: d16.dial-15.mbo.ma.ultra.net X-Complaints-To: abuse@ultra.net X-Ultra-Time: 15 Oct 1998 13:59:40 GMT X-Newsreader: News Xpress Version 1.0 Beta #4 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!news.maxwell.syr.edu!newsfeed.xcom.net!news.ultranet.com!d16 In article <3624C21E.5A2E@gazonk.del>, "Foobar T. Clown" wrote: >jmfbahciv@aol.com wrote: >> >> Are computers without interrupts interesting? And, if they are, >> how are/were they used? > >I used to program on engineering workstations with bit-mapped displays, >GUIs, mice, preemptive multi-tasking, and demand paged, protected, >virtual memory, but no interrupts... > >....Well, no interrupt HARDWARE, anyway. > >They were PERQs, made by Three Rivers Computer, Inc., in Pittsburgh PA. >The CPU was a clean, simple microcode engine with a writeable control >store. We ran microcode emulators for a UCSD-P-System-like instruction >set and, for a custom LISP instruction set. The only sense in which >there were interrupts was that both emulators would poll for certain >external conditions after completing each instruction, and would >appropriately alter the virtual machine context if an event occurred. > >When you wrote microcode for a PERQ, you had to be careful to poll the >vertical retrace bit often enough, and call a special microcode >subroutine when it was set, otherwise you'd loose the video signal. > >So how did it do I/O? Like any *REAL* computer, it had a separate I/O >processor and a separate network processor to take care of the ugly, bit >pushing. So you still had have an interrupt mechanism in order to do store anything. /BAH Sigh! - Subtract a hundred and four for e-mail. ###### Message-ID: <36260CE8.E60@gazonk.del> Date: Thu, 15 Oct 1998 10:55:36 -0400 From: "Foobar T. Clown" Reply-To: foobar@gazonk.del Organization: Blurp X-Mailer: Mozilla 3.01 (WinNT; I) MIME-Version: 1.0 Newsgroups: alt.folklore.computers Subject: Re: Computers without interrupts or DMA References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <3624C21E.5A2E@gazonk.del> <704v4c$k2u$4@strato.ultra.net> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit NNTP-Posting-Host: 198.133.110.49 X-Trace: 15 Oct 1998 10:55:46 -0500, 198.133.110.49 Lines: 15 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.belnet.be!news-raspail.gip.net!news-peer.gip.net!news.gsl.net!gip.net!ix.netcom.com!zeus.nomos.com!198.133.110.49 jmfbahciv@aol.com wrote: > > In article <3624C21E.5A2E@gazonk.del>, > "Foobar T. Clown" wrote: > > > > [...about PERQ computers...] > > So you still had have an interrupt mechanism in order to do > store anything. Well, it all depends on what you mean by "computers without interrupts." I'll let you form your own judgement whether the PERQ fit that category. It's main CPU did not have interrupt hardware, but it's high level programming languages allowed a program to be notified of asynchronous events, and it used a Z80 as an I/O processor. ###### From: jmfbahciv@aol.com Newsgroups: alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: Thu, 15 Oct 98 12:55:34 GMT Organization: UltraNet Communications, Inc. Lines: 48 Message-ID: <704vne$k2u$5@strato.ultra.net> References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <702gug$4iq$1@shadow.skypoint.net> NNTP-Posting-Host: d16.dial-15.mbo.ma.ultra.net X-Complaints-To: abuse@ultra.net X-Ultra-Time: 15 Oct 1998 14:09:50 GMT X-Newsreader: News Xpress Version 1.0 Beta #4 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.belnet.be!newsgate.cistron.nl!het.net!212.63.192.161.MISMATCH!newshub.bart.net!news.tele2.nl!newsfeed1.swip.net!swipnet!newshub.northeast.verio.net!newsfeed.xcom.net!news.ultranet.com!d16 In article <702gug$4iq$1@shadow.skypoint.net>, "George R. Gonzalez" wrote: > >Foobar T. Clown wrote in message <3624C21E.5A2E@gazonk.del>... >>jmfbahciv@aol.com wrote: >>> >>> Are computers without interrupts interesting? And, if they are, >>> how are/were they used? > > >If your computer is complex, interrupts can be very hard to handle. >When an interrupt occurs, it has to be possible to save the complete >machine state, and restore it after the interrupt. In a simple machine, >saving the state is no big deal-- just save a few registers. But what >about a really complex CPU, with multiple functional units, pipelining, >instruction pre-fetch...? The machine state becomes very complex, >requiring many bytes to be pushed onto the stack. Then there's the case >where the designer made a mistake, and some important bit of machine >state isnt saveable. This happened with the CDC Star, and they had to >manually redesign a considerable portion of the CPU to make the state >saveable. > >Also if you have a complex and expensive CPU, do you really want it to be >handling every trivial keyboard interrupt? Oh, my, yes. Especially in the cases where I goofed badly and want the processor to stop doing what I told it to do. Consider the command, DELETE *.* > You might opt to forget about >interrupts and have some other cheaper processor handle all the I/O. >This is the way the CDC 6000 series went. But doesn't that imply that the more expensive processor has the potential of sitting around all day doing nothing? And how does those cheaper processors handling all the I/O get the more expensive processor to pay attention. Actually, your scenario seems to only make sense if the more expensive processor is used as a compute-intensive device and not a computer; then that implies that the compute-intensive device has to have a mechanism that interrupts the requestor saying, "I'm all done and here's the results". /BAH Sigh! - Subtract a hundred and four for e-mail. ###### Message-ID: <36260FCD.2657@gazonk.del> Date: Thu, 15 Oct 1998 11:07:57 -0400 From: "Foobar T. Clown" Reply-To: foobar@gazonk.del Organization: Blurp X-Mailer: Mozilla 3.01 (WinNT; I) MIME-Version: 1.0 Newsgroups: alt.folklore.computers Subject: Re: Computers without interrupts or DMA References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <702gug$4iq$1@shadow.skypoint.net> <704vne$k2u$5@strato.ultra.net> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit NNTP-Posting-Host: 198.133.110.49 X-Trace: 15 Oct 1998 11:08:07 -0500, 198.133.110.49 Lines: 22 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!news.maxwell.syr.edu!ix.netcom.com!zeus.nomos.com!198.133.110.49 jmfbahciv@aol.com wrote: > > In article <702gug$4iq$1@shadow.skypoint.net>, > "George R. Gonzalez" wrote: > > You might opt to forget about > >interrupts and have some other cheaper processor handle all the I/O. > > But doesn't that imply that the more expensive processor has the > potential of sitting around all day doing nothing? And how does > those cheaper processors handling all the I/O get the more > expensive processor to pay attention. In a PERQ computer (mentioned in a different branch of this topic), The IOP could *NOT* get the main processor to pay attention. All it could do is set flags. It was the responsibility of software (usually microcode) on the main processor to periocicly examine the flags. As for sitting around all day doing nothing... What PC processor doesn't? I've got two Pentiums at my desk that spend all day and all night waiting for my every keystroke. They don't even have to generate their own video, they've each got an expensive and vastly underutilized "graphics accelerator" (i.e., processor) for that job. ###### From: jeverett@wwa.DEFEAT.UCE.BOTS.com (John Everett) Newsgroups: alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: 15 Oct 1998 14:39:34 GMT Organization: Everett Associates Lines: 18 Message-ID: <7051f6$nm3$1@hirame.wwa.com> References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com><3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net><361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at><6vlcoo$d8r@agora.dmz.khoral.com> <7020ga$qrm$1@strato.ultra.net> <70484i$sf6$1@news2.saix.net> NNTP-Posting-Host: poolf8-012.wwa.com Mime-Version: 1.0 Content-Type: Text/Plain; charset=US-ASCII X-Newsreader: WinVN 0.99.8 (x86 32bit) Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.belnet.be!newsgate.cistron.nl!het.net!newsfeed.wirehub.nl!btnet-peer!btnet!newsfeed.cwix.com!207.241.0.194!news.wwa.com!not-for-mail In article <70484i$sf6$1@news2.saix.net>, ricklugg@intekom.co.za.hmmm says... > >Even though the early 60's commercial systems may have had interrupts, iirc >they were not always made use of. I just stumbled upon this thread so this may have been covered before, but on the Honeywell H-200, interrupt was an option. Since the H-200 was designed as a direct replacement (although not a plug compatible) for the IBM 1401, I'd guess there were also 1401 models without an interrupt capability. -- jeverett@wwa.DEFEAT.UCE.BOTS.com (John Everett) http://www.wwa.com/~jeverett ^^^^^^^^^^^^^^^ Things have gotten so bad I feel the need to disguise my email address. And I don't like this explanation because I just hate long signatures. ###### Newsgroups: alt.folklore.computers Subject: Re: Computers without interrupts or DMA From: bmarcum@iglou.com X-Everything: Net-Tamer V 1.08X NNTP-Posting-Host: 204.255.239.30 X-NNTP-Posting-Host: 204.255.239.30 Message-ID: <36265766.0@news.iglou.com> Date: 15 Oct 1998 16:13:26 -0500 X-Trace: 15 Oct 1998 16:13:26 -0500, 204.255.239.30 Lines: 16 X-NNTP-Posting-Host: 192.107.41.52 Organization: IgLou Internet Services, Inc. Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.belnet.be!news-raspail.gip.net!news-peer.gip.net!news.gsl.net!gip.net!newsfeed.cwix.com!192.107.41.5!news.iglou.com!204.255.239.30 On 1998-10-14 shoppa@trailing-edge.com said: >You're mistakenly assuming that the ZX-80 can do a display refresh >while running user programs; you'll probably be surprised when I >tell you it can't! While doing the display refresh, the ZX-80 But the ZX-81 (aka Timex-Sinclair 1000) could. It slowed programs down tremendously, so the Basic had FAST and SLOW commands to control the display. >does nothing more than scan the keyboard for keypresses. And >while a user program (as opposed to the wait-for-keypress loop) >is running, the screen is completely blank. >Tim. Net-Tamer V 1.08X - Test Drive ###### From: ard@p850ug1.demon.co.uk (Tony Duell) Newsgroups: alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: 15 Oct 1998 20:11:50 +0100 Organization: P850 User Group Message-ID: <705hdm$kp@p850ug1.demon.co.uk> References: <3624C21E.5A2E@gazonk.del> NNTP-Posting-Host: p850ug1.demon.co.uk X-NNTP-Posting-Host: p850ug1.demon.co.uk:158.152.97.199 X-Trace: news.demon.co.uk 908488624 nnrp-04:16535 NO-IDENT p850ug1.demon.co.uk:158.152.97.199 X-Complaints-To: abuse@demon.net X-Newsreader: TIN [version 1.2 PL2] Lines: 70 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!newscore.univie.ac.at!europa.clark.net!198.138.0.5!newshub.northeast.verio.net!woodstock.news.demon.net!demon!news.demon.co.uk!demon!p850ug1.demon.co.uk!not-for-mail Foobar T. Clown (foobar@gazonk.del) wrote: : jmfbahciv@aol.com wrote: : > : > Are computers without interrupts interesting? And, if they are, : > how are/were they used? : I used to program on engineering workstations with bit-mapped displays, : GUIs, mice, preemptive multi-tasking, and demand paged, protected, : virtual memory, but no interrupts... : ...Well, no interrupt HARDWARE, anyway. : They were PERQs, made by Three Rivers Computer, Inc., in Pittsburgh PA. Actually, the PERQ (I assume you mean a classic-PERQ and not a 3a) does have some hardware support for interrupts. : The CPU was a clean, simple microcode engine with a writeable control : store. We ran microcode emulators for a UCSD-P-System-like instruction : set and, for a custom LISP instruction set. The only sense in which : there were interrupts was that both emulators would poll for certain : external conditions after completing each instruction, and would : appropriately alter the virtual machine context if an event occurred. Now... This is from memory, but if you like I'll check up the exact details in the CPU technical manual Sort-of... There were 8 interrupt lines coming in to the CPU board. If any one became active it asserted a particular condition code bit (like a flag). The microcode could check that bit and jump somewhere with a phrase like if intrpend call (service) Then, if the interupt line is asserted, the service routine would be called. The 8 interrupt lines go into a priority encoder. The 3-bit output from that went into the microcode jump logic. The service routine would be something like service: vector(intvec); intvec is a constant which was combined with the 3 bits from the priority encoder to produce the address of the (microcode) interrupt service routine for the highest-priority interrupt currently being received. So, in a sense the microcode did have to poll the interrupt lines, but there was a lot of support for this polling. I suspect that interrupts on other processors are sampled by the microcode - they are one some PDP11s for example. The difference is that the PERQ allows you to write that microcode yourself. : When you wrote microcode for a PERQ, you had to be careful to poll the : vertical retrace bit often enough, and call a special microcode : subroutine when it was set, otherwise you'd loose the video signal. : So how did it do I/O? Like any *REAL* computer, it had a separate I/O : processor and a separate network processor to take care of the ugly, bit : pushing. The I/O processor (a Z80) handles the low-speed I/O only - the keyboard, GPIB, serial ports, sound, floppies, RTC, mouse. The hard disk, ethernet, and laser printer are handled by the main PERQ CPU, although there's a powerful DMA controller to transfer data to/from main memory on the PERQ. You may wonder why I'm writing about a 19-year-old machine in the present tense. Well, I've got 3 of the fine machines here, still operational. -tony ###### From: hancock4@bbs.cpcn.com (Lisa or Jeff) Newsgroups: alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: 16 Oct 1998 02:39:36 GMT Organization: Net Access BBS Lines: 15 Message-ID: <706bl8$fm9@netaxs.com> NNTP-Posting-Host: bbs.cpcn.com Originator: root@bbs.cpcn.com Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!newscore.univie.ac.at!europa.clark.net!207.106.0.20!news-xfer.newsread.com!netaxs.com!newsread.com!netaxs.newsread.com!bbs.cpcn.com!root > I just stumbled upon this thread so this may have been covered before, but > on the Honeywell H-200, interrupt was an option. Since the H-200 was > designed as a direct replacement (although not a plug compatible) for the > IBM 1401, I'd guess there were also 1401 models without an interrupt > capability. AFAIK, the IBM 1401 didn't have any interrupt capability. The program could test sense switches and other conditions if so coded, but not set up to react if an external condition occured. The high end model, the 1410, had a bit more power, but I still don't think it had true interrupt handling capability. The H-200 was a threat to IBM and frightened them as they lost sales to it. It hustled them to get the S/360 out the door. ###### From: jmfbahciv@aol.com Newsgroups: alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: Sat, 17 Oct 98 11:08:40 GMT Organization: UltraNet Communications, Inc. Lines: 30 Message-ID: <70a27j$ros$1@strato.ultra.net> References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <36260FCD.2657@gazonk.del> NNTP-Posting-Host: d8.dial-11.mbo.ma.ultra.net X-Complaints-To: abuse@ultra.net X-Ultra-Time: 17 Oct 1998 12:23:15 GMT X-Newsreader: News Xpress Version 1.0 Beta #4 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!news.maxwell.syr.edu!newsfeed.xcom.net!news.ultranet.com!d8 In article <36260FCD.2657@gazonk.del>, "Foobar T. Clown" wrote: >jmfbahciv@aol.com wrote: >> >> In article <702gug$4iq$1@shadow.skypoint.net>, >> "George R. Gonzalez" wrote: >> > You might opt to forget about >> >interrupts and have some other cheaper processor handle all the I/O. >> >> But doesn't that imply that the more expensive processor has the >> potential of sitting around all day doing nothing? And how does >> those cheaper processors handling all the I/O get the more >> expensive processor to pay attention. > >In a PERQ computer (mentioned in a different branch of this topic), The >IOP could *NOT* get the main processor to pay attention. All it could >do is set flags. It was the responsibility of software (usually >microcode) on the main processor to periocicly examine the flags. > >As for sitting around all day doing nothing... What PC processor >doesn't? I've got two Pentiums at my desk that spend all day and all >night waiting for my every keystroke. They don't even have to generate >their own video, they've each got an expensive and vastly underutilized >"graphics accelerator" (i.e., processor) for that job. Timesharing solved wasted CPU cycles a long time ago. /BAH Subtract a hundred and four for e-mail. ###### From: sam@greenaum.demonARSE!ARSE!ARSE!.co.uk (Sam.) Newsgroups: comp.sys.ibm.pc.hardware.systems,alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: Sun, 18 Oct 1998 06:07:44 GMT Organization: Rossum's Universal Robots Message-ID: <362d85ac.751123@158.152.254.68> References: <3624B05B.59F5F0CF@trailing-edge.com> <703l9j$89g@newsops.execpc.com> <908454980.293.0.nnrp-10.9e9878e0@news.demon.co.uk> Reply-To: sam@greenaum.demonARSE!ARSE!ARSE!.co.uk NNTP-Posting-Host: greenaum.demon.co.uk X-NNTP-Posting-Host: greenaum.demon.co.uk:194.222.71.189 X-Trace: news.demon.co.uk 908690942 nnrp-04:16657 NO-IDENT greenaum.demon.co.uk:194.222.71.189 X-Complaints-To: abuse@demon.net X-Newsreader: Forte Agent 1.5/32.452 X-No-Archive: yes MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 48 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.belnet.be!news-raspail.gip.net!news-lond.gip.net!news.gsl.net!gip.net!dispose.news.demon.net!demon!news.demon.co.uk!demon!greenaum.demon.co.uk!not-for-mail On Thu, 15 Oct 1998 12:36:20 GMT, dg@ (David Given) sprachen: >Would it be possible to make a ZX81 or Spectrum clone from one of these? I don't know, but get thyself to comp.sys.sinclair. I do know that you can get complete Z80s, up to 20MHz, implemented as parts on modern ULAs. Some of comp.sys.sinclair are working on a new ZX, a successor to the Spectrum which used many ingenious tricks to get a colour computer with 1-bit sound out of cheap hardware. The new one is going to have some sort of super-processor, an LCD, USB etc and yet somehow be cheap enough to be worthwhile. An alternative course was to clone the Spectrum into a sort of Gameboy, with a small LCD, and put it's massive library of 10,000-ish games onto ROM chips or something. If you feel like doing this one cheap enough I'd buy one. Speccy games are archived on the net as complete snapshots of the machine state, so would be easy enough to load in. Also the ZX81 didn't get it's 60Hz interrupt from the mains, it would be a bit unreliable for starters, as well as impossible cos it took a 9V DC supply. It probably came from the system clock. It was possible to turn it off to give your programs the other 80% of the CPU's time. And because the screen was generated more-or-less by software, better programmers managed to almost get hi-res graphics out of it, actually they just jumped to different places in the character set in ROM on each scanline. >All the hard stuff has already been done (not that ZX81's are very >complex). You'd need to fake up the custom chips somehow. It's about 40 ICs worth of logic gates, it's been done by some hackers in Germany. It's probably one of the best supported 8-bits, ridiculously enough. The Atari 2600 is another interesting one, having no graphics memory at all, just a couple of 8-bit sprite registers, a 20-bit playfield registers, a 1-bit ball and 2 2-bit missiles, you draw on the freaking thing by setting up the registers for each scanline, then executing a store that freezes the 6502 til the start of the next scanline. It's comical how badly some of the 70s and 80s arcade games were translated to it. -------------------------------------------------------------------- Digital TV, that's what. 300 channels. Shite for all. Shite for every household.A democracy of shite. http://www.greenaum.demon.co.uk/ ... ###### From: "Lonnie L. Filbrun" Newsgroups: comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.soundcard.advocacy,comp.sys.ibm.pc.soundcard.tech,comp.sys.ibm.pc.hardware.chips,alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: Tue, 20 Oct 1998 23:40:06 -0700 Organization: Frontier GlobalCenter Inc. Lines: 16 Message-ID: <70jve3$dfd$1@nnrp02.primenet.com> References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <3624B05B.59F5F0CF@trailing-edge.com> NNTP-Posting-Host: ip-22-075.phx.primenet.com X-Complaints-To: abuse@globalcenter.net X-Posted-By: @206.165.22.75 (lfil) X-Newsreader: Microsoft Outlook Express 4.72.2106.4 X-Mimeole: Produced By Microsoft MimeOLE V4.72.2106.4 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.belnet.be!news-raspail.gip.net!news-peer.gip.net!news.gsl.net!gip.net!dca1-hub1.news.digex.net!digex!nntp.primenet.com!news.primenet.com!not-for-mail Thats also why the screen flickerd after every key press!!! -Lonnie Tim Shoppa wrote in message <3624B05B.59F5F0CF@trailing-edge.com>... > >You're mistakenly assuming that the ZX-80 can do a display refresh >while running user programs; you'll probably be surprised when I >tell you it can't! While doing the display refresh, the ZX-80 >does nothing more than scan the keyboard for keypresses. And >while a user program (as opposed to the wait-for-keypress loop) >is running, the screen is completely blank. > >Tim. ###### From: Marcin Nowak Newsgroups: comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.soundcard.advocacy,comp.sys.ibm.pc.soundcard.tech,comp.sys.ibm.pc.hardware.chips,alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: 21 Oct 1998 09:39:19 +0200 Organization: CERN - European Laboratory for Particle Physics Lines: 26 Message-ID: References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <3624B05B.59F5F0CF@trailing-edge.com> <70jve3$dfd$1@nnrp02.primenet.com> NNTP-Posting-Host: pcitasd15.cern.ch X-Trace: sunnews.cern.ch 908955561 11032 (None) 137.138.38.15 X-Complaints-To: news@sunnews.cern.ch X-Newsreader: Gnus v5.3/Emacs 19.34 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!cern.ch!news The screen flickers not after every key press, but only when typing in programs in BASIC. When the programs run, there definitly is no flicker and screen refresh is working, no matter how many keys you press. I have been playing games on ZX-81 for years and some of them were for ZX-80. You could not play if you were not able to see the screen when the game run, could you? Marcin "Lonnie L. Filbrun" writes: > Thats also why the screen flickerd after every key press!!! > > -Lonnie > > Tim Shoppa wrote in message <3624B05B.59F5F0CF@trailing-edge.com>... > > > >You're mistakenly assuming that the ZX-80 can do a display refresh > >while running user programs; you'll probably be surprised when I > >tell you it can't! While doing the display refresh, the ZX-80 > >does nothing more than scan the keyboard for keypresses. And > >while a user program (as opposed to the wait-for-keypress loop) > >is running, the screen is completely blank. > > > >Tim. > ###### From: info@fdhoekstra.nl Newsgroups: comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.soundcard.advocacy,comp.sys.ibm.pc.soundcard.tech,comp.sys.ibm.pc.hardware.chips,alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: Wed, 21 Oct 1998 15:28:25 +0200 Organization: Drukkerij Uitgeverij F. D. Hoekstra bv Lines: 27 Message-ID: <362DE179.33F8@fdhoekstra.nl> References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <3624B05B.59F5F0CF@trailing-edge.com> <70jve3$dfd$1@nnrp02.primenet.com> NNTP-Posting-Host: zwl1-p123.worldonline.nl Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Mailer: Mozilla 3.01Gold (Win95; I) Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.belnet.be!newsgate.cistron.nl!het.net!news.worldonline.nl!not-for-mail Marcin Nowak wrote: > "Lonnie L. Filbrun" writes: > > Thats also why the screen flickerd after every key press!!! > > Tim Shoppa wrote in message <3624B05B.59F5F0CF@trailing-edge.com>... > > > > > >You're mistakenly assuming that the ZX-80 can do a display refresh > > >while running user programs; you'll probably be surprised when I > > >tell you it can't! While doing the display refresh, the ZX-80 > > >does nothing more than scan the keyboard for keypresses. And > > >while a user program (as opposed to the wait-for-keypress loop) > > >is running, the screen is completely blank. > > The screen flickers not after every key press, but only when typing > in programs in BASIC. When the programs run, there definitly is no > flicker and screen refresh is working, no matter how many keys you > press. I have been playing games on ZX-81 for years and some of them > were for ZX-80. You could not play if you were not able to see the > screen when the game run, could you? Isn't it that _before_ every keyscan, the screen is refreshed? This would be at every timer interrupt, or on demand, depending on the program. This way it would show, but flicker in Basic; you'd be able to play games because they continually scan the keyboard, and any other programs that just sit there and buzz would show up blank, and refresh only when ready for input. Richard ###### Message-ID: <362DB12E.B108230@trailing-edge.com> From: Tim Shoppa Organization: Trailing Edge Technology X-Mailer: Mozilla 3.03Gold (X11; I; OpenVMS V7.0 DEC 3000 Model 300L) MIME-Version: 1.0 Newsgroups: comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.soundcard.advocacy,comp.sys.ibm.pc.soundcard.tech,comp.sys.ibm.pc.hardware.chips,alt.folklore.computers Subject: Re: Computers without interrupts or DMA References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <3624B05B.59F5F0CF@trailing-edge.com> <70jve3$dfd$1@nnrp02.primenet.com> <362DE179.33F8@fdhoekstra.nl> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 43 Date: Wed, 21 Oct 1998 10:02:22 -0400 NNTP-Posting-Host: 198.232.144.27 X-Trace: audrey2.cais.com 908979054 198.232.144.27 (Wed, 21 Oct 1998 10:10:54 EDT) NNTP-Posting-Date: Wed, 21 Oct 1998 10:10:54 EDT Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.belnet.be!newsgate.cistron.nl!het.net!news-feed.inet.tele.dk!bofh.vszbr.cz!cpk-news-hub1.bbnplanet.com!news.bbnplanet.com!news-peer.sprintlink.net!news-backup-east.sprintlink.net!news.sprintlink.net!205.177.10.1!in1.nntp.cais.net!199.0.216.204.MISMATCH!audrey2.cais.com!not-for-mail info@fdhoekstra.nl wrote: > > Marcin Nowak wrote: > > "Lonnie L. Filbrun" writes: > > > Thats also why the screen flickerd after every key press!!! > > > Tim Shoppa wrote in message <3624B05B.59F5F0CF@trailing-edge.com>... > > > > > > > >You're mistakenly assuming that the ZX-80 can do a display refresh > > > >while running user programs; you'll probably be surprised when I > > > >tell you it can't! While doing the display refresh, the ZX-80 > > > >does nothing more than scan the keyboard for keypresses. And > > > >while a user program (as opposed to the wait-for-keypress loop) > > > >is running, the screen is completely blank. > > > > The screen flickers not after every key press, but only when typing > > in programs in BASIC. When the programs run, there definitly is no > > flicker and screen refresh is working, no matter how many keys you > > press. I have been playing games on ZX-81 for years and some of them > > were for ZX-80. You could not play if you were not able to see the > > screen when the game run, could you? > > Isn't it that _before_ every keyscan, the screen is refreshed? > This would be at every timer interrupt, or on demand, depending > on the program. Timer interrupt? What timer interrupts? We're talking about ZX-80's here. > This way it would show, but flicker in Basic; > you'd be able to play games because they continually scan the > keyboard, and any other programs that just sit there and buzz > would show up blank, and refresh only when ready for input. Nope, ZX-80 programs exist which continually scan the keyboard but do not display anything. Unless you go to great pains to refresh the screen exactly when it needs refreshing, you get garbage. (And the folks who wrote live-action video games for them were truly masters of counting Z-80 clock cycles!) I highly recommend Don Lancaster's _Cheap Video Cookbook_ if you want to see details about CPU-based-screen-refresh schemes. Tim. ###### From: Ken Smith Newsgroups: comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.soundcard.advocacy,comp.sys.ibm.pc.soundcard.tech,comp.sys.ibm.pc.hardware.chips,alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: 21 Oct 1998 13:57:39 GMT Organization: a2i network Lines: 27 Message-ID: <70kp8j$77e$1@samba.rahul.net> References: <3624B05B.59F5F0CF@trailing-edge.com> <70jve3$dfd$1@nnrp02 NNTP-Posting-Host: waltz.rahul.net NNTP-Posting-User: kensmith Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!isdnet!newsfeed.nyu.edu!newsfeed.direct.ca!su-news-hub1.bbnplanet.com!news.bbnplanet.com!news.pbi.net!bug.rahul.net!samba.rahul.net!rahul.net!a2i!kensmith.a2i!kensmith In article , Marcin Nowak wrote: > > The screen flickers not after every key press, but only when typing >in programs in BASIC. When the programs run, there definitly is no >flicker and screen refresh is working, no matter how many keys you >press. I have been playing games on ZX-81 for years and some of them >were for ZX-80. You could not play if you were not able to see the >screen when the game run, could you? This is not true of the ZX80. The ZX81 had the "fast" and "slow" modes. The ZX80 was always in "fast" mode. In fast mode the screen refresh stopped when the program was running. In the ZX80 the code took the address of what was to be displayed, set the MSB, and jumped to that location. U14 and 2 sections of U15 forced the bus to the Z80 to be zeros (a nop) when ever any instruction other than a halt was fetched from 8000H or higher. The INT was wired to A6 so that the refresh register could be used to count off bytes till the horz. sync pulse. This meant that the CPU was very busy making the display and there was very little time left over for the running of the program in "slow" mode. -- -- kensmith@rahul.net forging knowledge ###### From: Marcin Nowak Newsgroups: comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.soundcard.advocacy,comp.sys.ibm.pc.soundcard.tech,comp.sys.ibm.pc.hardware.chips,alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: 21 Oct 1998 19:41:47 +0200 Organization: CERN - European Laboratory for Particle Physics Lines: 60 Message-ID: References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <3624B05B.59F5F0CF@trailing-edge.com> <70jve3$dfd$1@nnrp02.primenet.com> <362DE179.33F8@fdhoekstra.nl> <362DB12E.B108230@trailing-edge.com> NNTP-Posting-Host: pcitasd15.cern.ch X-Trace: sunnews.cern.ch 908991703 27324 (None) 137.138.38.15 X-Complaints-To: news@sunnews.cern.ch X-Newsreader: Gnus v5.3/Emacs 19.34 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!cern.ch!news Hm, I do not have first-hand experience with ZX-80, but I can assure you that for ZX-81 there was no problem with live-action video games. I have written some in assembler and there was nothing concerning refresh. The only thing that used clock-counting were pseudo-hi-res games, but that is different matter. And I remember that Z80 had a pair of interrupt registers called IR and that in ZX-81 there was an external (to cpu) source of interrupts - I think we can call it a timer or clock. And the flicker on the screen when entering BASIC program was not because the interrupts were software driven, but because the refresh was done by cpu and was disabled when doing intensive task, like, entering a line of BASIC program. Marcin Tim Shoppa writes: > info@fdhoekstra.nl wrote: > > > > Marcin Nowak wrote: > > > "Lonnie L. Filbrun" writes: > > > > Thats also why the screen flickerd after every key press!!! > > > > Tim Shoppa wrote in message <3624B05B.59F5F0CF@trailing-edge.com>... > > > > > > > > > >You're mistakenly assuming that the ZX-80 can do a display refresh > > > > >while running user programs; you'll probably be surprised when I > > > > >tell you it can't! While doing the display refresh, the ZX-80 > > > > >does nothing more than scan the keyboard for keypresses. And > > > > >while a user program (as opposed to the wait-for-keypress loop) > > > > >is running, the screen is completely blank. > > > > > > The screen flickers not after every key press, but only when typing > > > in programs in BASIC. When the programs run, there definitly is no > > > flicker and screen refresh is working, no matter how many keys you > > > press. I have been playing games on ZX-81 for years and some of them > > > were for ZX-80. You could not play if you were not able to see the > > > screen when the game run, could you? > > > > Isn't it that _before_ every keyscan, the screen is refreshed? > > This would be at every timer interrupt, or on demand, depending > > on the program. > > Timer interrupt? What timer interrupts? We're talking about > ZX-80's here. > > > This way it would show, but flicker in Basic; > > you'd be able to play games because they continually scan the > > keyboard, and any other programs that just sit there and buzz > > would show up blank, and refresh only when ready for input. > > Nope, ZX-80 programs exist which continually scan the keyboard > but do not display anything. Unless you go to great pains to > refresh the screen exactly when it needs refreshing, you get > garbage. (And the folks who wrote live-action video games for > them were truly masters of counting Z-80 clock cycles!) > > I highly recommend Don Lancaster's _Cheap Video Cookbook_ if you > want to see details about CPU-based-screen-refresh schemes. > > Tim. ###### From: info@fdhoekstra.nl Newsgroups: comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.soundcard.advocacy,comp.sys.ibm.pc.soundcard.tech,comp.sys.ibm.pc.hardware.chips,alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: Thu, 22 Oct 1998 09:58:17 +0200 Organization: Drukkerij Uitgeverij F. D. Hoekstra bv Lines: 34 Message-ID: <362EE599.2312@fdhoekstra.nl> References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <3624B05B.59F5F0CF@trailing-edge.com> <70jve3$dfd$1@nnrp02.primenet.com> <362DE179.33F8@fdhoekstra.nl> <362DB12E.B108230@trailing-edge.com> NNTP-Posting-Host: zwl1-p79.worldonline.nl Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Mailer: Mozilla 3.01Gold (Win95; I) Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.belnet.be!newsgate.cistron.nl!het.net!news.worldonline.nl!not-for-mail Tim Shoppa wrote: > > info@fdhoekstra.nl wrote: > > > > Marcin Nowak wrote: > > > "Lonnie L. Filbrun" writes: > > > > Thats also why the screen flickerd after every key press!!! > > > > Tim Shoppa wrote in message <3624B05B.59F5F0CF@trailing-edge.com>... > > > > > > > > > >You're mistakenly assuming that the ZX-80 can do a display refresh > > > > >while running user programs; you'll probably be surprised when I > > > > >tell you it can't! While doing the display refresh, the ZX-80 > > > > >does nothing more than scan the keyboard for keypresses. And > > > > >while a user program (as opposed to the wait-for-keypress loop) > > > > >is running, the screen is completely blank. > > > > > > The screen flickers not after every key press, but only when typing > > > in programs in BASIC. When the programs run, there definitly is no > > > flicker and screen refresh is working, no matter how many keys you > > > press. I have been playing games on ZX-81 for years and some of them > > > were for ZX-80. You could not play if you were not able to see the > > > screen when the game run, could you? > > > > Isn't it that _before_ every keyscan, the screen is refreshed? > > This would be at every timer interrupt, or on demand, depending > > on the program. > > Timer interrupt? What timer interrupts? We're talking about > ZX-80's here. Yes, you're right; I'm probably confusing the thing with ZX-81's and Speccies here. Velly solly. Richard ###### Message-ID: <362E80E1.61206B83@yahoo.com> Date: Wed, 21 Oct 1998 17:48:33 -0700 From: "Gregg E." X-Mailer: Mozilla 4.06 [en]C-DIAL (Win95; U) MIME-Version: 1.0 Newsgroups: comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.soundcard.advocacy,comp.sys.ibm.pc.soundcard.tech,comp.sys.ibm.pc.hardware.chips,alt.folklore.computers Subject: Re: Computers without interrupts or DMA References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <3624B05B.59F5F0CF@trailing-edge.com> <70jve3$dfd$1@nnrp02.primenet.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit NNTP-Posting-Host: 208.8.247.20 Lines: 29 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.belnet.be!news-raspail.gip.net!news-peer.gip.net!news.gsl.net!gip.net!howland.erols.net!news-peer.sprintlink.net!news-backup-east.sprintlink.net!news.sprintlink.net!205.162.184.12!news.rmci.net!208.8.247.20 Hehe, he must have always run in "fast" mode... Marcin Nowak wrote: > > The screen flickers not after every key press, but only when typing > in programs in BASIC. When the programs run, there definitly is no > flicker and screen refresh is working, no matter how many keys you > press. I have been playing games on ZX-81 for years and some of them > were for ZX-80. You could not play if you were not able to see the > screen when the game run, could you? > > Marcin > > "Lonnie L. Filbrun" writes: > > Thats also why the screen flickerd after every key press!!! > > > > -Lonnie > > > > Tim Shoppa wrote in message <3624B05B.59F5F0CF@trailing-edge.com>... > > > > > >You're mistakenly assuming that the ZX-80 can do a display refresh > > >while running user programs; you'll probably be surprised when I > > >tell you it can't! While doing the display refresh, the ZX-80 > > >does nothing more than scan the keyboard for keypresses. And > > >while a user program (as opposed to the wait-for-keypress loop) > > >is running, the screen is completely blank. > > > > > >Tim. > > ###### From: "Andrew Cadley" Newsgroups: comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.soundcard.advocacy,comp.sys.ibm.pc.soundcard.tech,comp.sys.ibm.pc.hardware.chips,alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: Sun, 25 Oct 1998 01:34:17 +0100 Organization: University of East Anglia, Norwich, Norfolk, NR47TJ, UK Lines: 17 Message-ID: <70tv9g$kn4@cpca3.uea.ac.uk> References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <3624B05B.59F5F0CF@trailing-edge.com> <70jve3$dfd$1@nnrp02.primenet.com> <362DE179.33F8@fdhoekstra.nl> <362DB12E.B108230@trailing-edge.com> <362EE599.2312@fdhoekstra.nl> NNTP-Posting-Host: oak6d.vlg1.uea.ac.uk X-Newsreader: Microsoft Outlook Express 4.72.2120.0 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.2120.0 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news.belnet.be!news-raspail.gip.net!news-peer.gip.net!news.gsl.net!gip.net!cpk-news-hub1.bbnplanet.com!news.news.gtei.net!rill.news.pipex.net!pipex!server1.netnews.ja.net!cpca3.uea.ac.uk!news info@fdhoekstra.nl wrote in message <362EE599.2312@fdhoekstra.nl>... :Tim Shoppa wrote: :> Timer interrupt? What timer interrupts? We're talking about :> ZX-80's here. : :Yes, you're right; I'm probably confusing the thing with :ZX-81's and Speccies here. Velly solly. Speccys only had one interrupt at the start of the frame, no timers anywhere. AndyC ###### From: Ken Smith Newsgroups: comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.soundcard.advocacy,comp.sys.ibm.pc.soundcard.tech,comp.sys.ibm.pc.hardware.chips,alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: 25 Oct 1998 17:38:24 GMT Organization: a2i network Lines: 23 Message-ID: <70vnmg$ckc$1@samba.rahul.net> References: <3624B05B.59F5F0CF@trailing-edge.com> <70jve3$dfd$1@nnrp02 <70tv9g$kn4@cpca3.uea.ac.uk> NNTP-Posting-Host: waltz.rahul.net NNTP-Posting-User: kensmith Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!news.maxwell.syr.edu!news-peer.gip.net!news.gsl.net!gip.net!nntp.abs.net!news.mcs.net!ddsw1!bug.rahul.net!samba.rahul.net!rahul.net!a2i!kensmith.a2i!kensmith In article <70tv9g$kn4@cpca3.uea.ac.uk>, Andrew Cadley wrote: > >info@fdhoekstra.nl wrote in message <362EE599.2312@fdhoekstra.nl>... >:Tim Shoppa wrote: > >:> Timer interrupt? What timer interrupts? We're talking about >:> ZX-80's here. >: >:Yes, you're right; I'm probably confusing the thing with >:ZX-81's and Speccies here. Velly solly. > > >Speccys only had one interrupt at the start of the frame, no timers >anywhere. There were 2 interrupts. The INT and NMI interrupts where used. NMI was needed as part of the slow mode circuit. -- -- kensmith@rahul.net forging knowledge ###### From: "Andrew Cadley" Newsgroups: comp.sys.ibm.pc.hardware.systems,comp.sys.ibm.pc.soundcard.advocacy,comp.sys.ibm.pc.soundcard.tech,comp.sys.ibm.pc.hardware.chips,alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: Sun, 25 Oct 1998 19:55:43 -0000 Organization: University of East Anglia, Norwich, Norfolk, NR47TJ, UK Lines: 22 Message-ID: <70vvqt$u99@cpca3.uea.ac.uk> References: <3624B05B.59F5F0CF@trailing-edge.com> <70jve3$dfd$1@nnrp02 <70tv9g$kn4@cpca3.uea.ac.uk> <70vnmg$ckc$1@samba.rahul.net> NNTP-Posting-Host: oak6d.vlg1.uea.ac.uk X-Newsreader: Microsoft Outlook Express 4.72.2120.0 X-MimeOLE: Produced By Microsoft MimeOLE V4.72.2120.0 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!nntprelay.mathworks.com!newsfeed.cwix.com!158.43.192.17!rill.news.pipex.net!pipex!server1.netnews.ja.net!cpca3.uea.ac.uk!news Ken Smith wrote in message <70vnmg$ckc$1@samba.rahul.net>... :In article <70tv9g$kn4@cpca3.uea.ac.uk>, :Andrew Cadley wrote: :>Speccys only had one interrupt at the start of the frame, no timers :>anywhere. : :There were 2 interrupts. The INT and NMI interrupts where used. NMI was :needed as part of the slow mode circuit. Not on the Spectrum it wasn't. The video display was drawn by the ULA. In fact NMIs don't even work properly on the spectrum due to a bug in the ROM. They were used by the ZX81 though to do SLOW mode though. The only spectrum hardware which uses them AFAIK is the multiface, which placed its own ROM at 0000h as part of the interrupt acknowledge cycle. AndyC ###### From: spam.from.web@engelmeier.com (Thomas Engelmeier) Newsgroups: alt.folklore.computers Subject: Re: Computers without interrupts or DMA Date: Sun, 1 Nov 1998 19:37:11 +0100 Organization: University of Rostock Lines: 34 Message-ID: <1dhtwcf.18vqxn41j75uteN@[192.168.100.1]> References: <36092ddc.9244114@news.vpn.at> <6uln7s$3ad@web.nmti.com> <3624347a.22397202@news.vpn.at> <36173545.40593367@news.garden.net> <361DC83B.1E7C0E04@home.com> <36441857.365679098@gateway.axioma.co.at> <6vlcoo$d8r@agora.dmz.khoral.com> <3624B05B.59F5F0CF@trailing-edge.com> <70jve3$dfd$1@nnrp02.primenet.com> <362DE179.33F8@fdhoekstra.nl> <362DB12E.B108230@trailing-edge.com> <362EE599.2312@fdhoekstra.nl> <70tv9g$kn4@cpca3.uea.ac.uk> <70vnmg$ckc$1@samba.rahul.net> NNTP-Posting-Host: isdn-dialin20.lcm.de X-Newsreader: MacSOUP 2.3.3 (unregistered for 413 days) Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!news-fra1.dfn.de!fu-berlin.de!informatik.uni-rostock.de!tom Ken Smith wrote: > >Speccys only had one interrupt at the start of the frame, no timers > >anywhere. > > There were 2 interrupts. The INT and NMI interrupts where used. NMI was > needed as part of the slow mode circuit. F'Uped - this doesn't have anything to do with ibm - PC's. The /NMI was pulled up to 5 V with an 10 k resistor and connected to the interface slot, as was the /reset. NMI and RESET were later used for cracking games; i.e. multiface placed it's own ROM and saved the whole memory when an NMI occured while ISO-ROM (an replacement ROM) jumped to a fine (at this time; it's pretty basic compared even to MacsBug) disassembler. Interface1 just superceeded the built in ROM with it's own stuff at certain occasions. The /INT (only one level) was connected to and generated by the ULA at VBL (or HBL??) time, which allowed proper game timing. Back to the ZX-81, the NMI also wasn't used. The /INT was generated at the start of every screen line; in fast mode, it was masked out (no display - full calculating speed). During the line display, the character in rom for (screenbase + currpos) was generated. By mangling the rombase pointer to other ROM locations later "High res" graphics were possible by reassigning the character-Baseaddress in ROM for eight pixels. Well, nice memories.. My first computer .. and the first floppy... on the Spectrum... Ciao, TomE