From: "river" Newsgroups: alt.folklore.computers Subject: Old Microprocessors Date: 22 Feb 1999 10:58:58 GMT Organization: The Zipsters Lines: 16 Message-ID: <01be5e4a$ef9590e0$8512083d@Lockheed> NNTP-Posting-Host: 61.8.18.133 X-Newsreader: Microsoft Internet News 4.70.1155 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!newscore.univie.ac.at!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!intgwpad.nntp.telstra.net!news1.optus.net.au!optus!newsfeed.zip.com.au!the-fly.zip.com.au!not-for-mail Hi, How do I convert 20mA current-loop to RS232C? I got an old SC/MP and old 2650 SBCs that I'd like to fire up. Also, I got another 2650 system that needs an ASCII keyboard. I have programmed an old AIM-65 to be a keyboard, but I'd rather get a dedicated keyboard. Are there any ASCII kbds around anymore? Is it possible to use some circuit to convert the output of a PC kbd to ASCII? Any ideas? river ###### From: Robert Billing Newsgroups: alt.folklore.computers Subject: Re: Old Microprocessors Date: Mon, 22 Feb 1999 19:22:25 +0000 Organization: Tanglewood Message-ID: <36D1AE71.EA6C2924@tnglwood.demon.co.uk> References: <01be5e4a$ef9590e0$8512083d@Lockheed> NNTP-Posting-Host: localhost.demon.co.uk X-NNTP-Posting-Host: tnglwood.demon.co.uk:158.152.132.30 X-Trace: news.demon.co.uk 919711985 nnrp-08:26428 NO-IDENT tnglwood.demon.co.uk:158.152.132.30 X-Complaints-To: abuse@demon.net Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Mailer: Mozilla 4.07 [en] (X11; I; Linux 2.0.31 i586) Lines: 14 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!news.belnet.be!news-feed.inet.tele.dk!bofh.vszbr.cz!news-lond.gip.net!news.gsl.net!gip.net!newspeer.clara.net!news.clara.net!dispose.news.demon.net!demon!news.demon.co.uk!demon!tnglwood.demon.co.uk!not-for-mail river wrote: > How do I convert 20mA current-loop to RS232C? I got an old SC/MP and > old 2650 SBCs that I'd like to fire up. Analogue devices do some line driver and receiver chips, couple these to any old RS232 transceiver. You'll have to design some analogue circuitry, but nothing difficult. -- I am Robert Billing, Christian, inventor, traveller, cook and animal lover, I live near 0:46W 51:22N. http://www.tnglwood.demon.co.uk/ "Bother," said Pooh, "Eeyore, ready two photon torpedoes and lock phasers on the Heffalump, Piglet, meet me in transporter room three" ###### From: don@news.daedalus.co.nz (Don Stokes) Newsgroups: alt.folklore.computers Subject: Re: Old Microprocessors Date: 22 Feb 1999 22:06:09 GMT Organization: Daedalus Consulting Lines: 83 Message-ID: <7askch$rik$1@news.wlg.netlink.net.nz> References: <01be5e4a$ef9590e0$8512083d@Lockheed> <36D1AE71.EA6C2924@tnglwood.demon.co.uk> NNTP-Posting-Host: toyunix.zl2tnm.gen.nz Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!isdnet!newsfeed.cwix.com!203.97.37.7!newsfeed.clear.net.nz!news.wlg.netlink.net.nz!don river wrote: > How do I convert 20mA current-loop to RS232C? I got an old SC/MP and > old 2650 SBCs that I'd like to fire up. It depends which end the SBCs think they are. Current loops have three components, a current source, a current detector and a transmitter. The "obvious" thing to do would be to attach the current source to the transmitter (which is essentially the approach used in RS232, except it's voltage that's regulated not current), but since 20mA comes from telegraphy, it's not done that way -- both loops are usually powered from the same end, so the remote device doesn't introduce power into the (network provider's) loop. The remote device then only needs to be in essence a solenoid for the receiver and a switch for the transmitter. The effect is that you have "active" and "passive" current loops interfaces, the "active" end being the one providing current. Usually it's the "host" end that does this, with terminals as the passive elements in the loops. That said, what follows is the comments from a bit of code I did to get a Teletype ASR33 talking to a VAX. This is very much in the "it worked for me" category... ; This little ditty is used to emulate a 20mA interface using an RS232 ; port and the following circuit: ; ; RS232 20mA Passive Interface ; 100 ; TXD --/\/\---------//------------ RX- ; ; GND --->|----------//------------ RX+ ; ; RTS ---------------//------------ TX- ; ; RXD --------+------//------------ TX+ ; | ; DTR --/\/\--+ ; 1k ; ; The way this works is that the transmit loop (RX at the other end) ; current is provided via the TX and GND via a 100 ohm current ; limiting resistor. ; ; The receive side of this is a bit trickier; RTS is held low (-6V) ; to provide a constant mark to RXD as long as the remote interface ; holds the line closed. DTR is held high (+6V) and connected to RXD ; via a 1k resistor, so when the remote interface opens the line to ; transmits a space symbol, the line is biased by the DTR connection, ; which pulls the RXD line to a space (+6V) state. ; ; For this to work, DTR and RTS must be held high and low respectively, ; not a normal state for RS232 ports under VMS. Fortunately, as long ; as the port isn't in MODEM or COMMSYNC modes, VMS ignores the control ; signal states; we just need to prod them into the state we want and ; leave it at that. ; ; Note: the above is not a true 20mA interface; it makes the following ; assumptions: ; ; The line is local, ie transmission line loss is negligible; ; Transmit does not in any way detect current flow; ; The receive interface has a low (<100 ohm) impedance; ; Line/transmitter/receiver impedances remain constant. ; ; The above circuit could be made more adaptable by replacing the 100 ; ohm resistor with a potentiometer, allowing the circuit to be ; adapted for longer transmission lines etc. However it is not by ; any stretch of the imagination a universal 20mA converter. Note that the above was designed around the sort of characteristics found on DEC serial interfaces. These tend to operate on the lower voltage/higher current end of the RS232 spec, +/-6V. I think a dead short TX-GND got about 50mA through. A multimeter is your friend for this sort of thing. 8-) If the interface is active, the above won't work. You'll need to design something or buy a converter. B&B Electronics (www.bb-elec.com) sell a series of simple 20mA converters at reasonable prices if you don't feel like designing it yourself. -- Don Stokes, Networking Consultant http://www.daedalus.co.nz +64 25 739 724 ###### From: cjt&trefoil Newsgroups: alt.folklore.computers Subject: Re: Old Microprocessors Date: Mon, 01 Mar 1999 21:33:13 -0600 Organization: Prodigy Services Corp Lines: 33 Message-ID: <36DB5BF8.6041@prodigy.net> References: <01be5e4a$ef9590e0$8512083d@Lockheed> <36DB28CB.8629F8D6@flash.net> Reply-To: cheljuba@prodigy.net NNTP-Posting-Host: dllsb505-17.splitrock.net Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Post-Time: 2 Mar 1999 03:33:48 GMT X-Auth-User: 002709921/f4cb21d0fedb160a X-Problems-To: abuse@prodigy.net X-Mailer: Mozilla 3.04 (Win95; U) Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!newsfeed-zh.ip-plus.net!news.ip-plus.net!News.Amsterdam.UnisourceCS!skynet.be!newscon05!prodigy.com!not-for-mail Richard Lamb wrote: > > I'd like to have one of those old AIM-65's! > Add one to my little collection... > > Anybody wanna part with one? > > email lamb01@flash.net > > Richard Lamb > > river wrote: > > > > Hi, > > > > How do I convert 20mA current-loop to RS232C? I got an old SC/MP and > > old 2650 SBCs that I'd like to fire up. > > > > Also, I got another 2650 system that needs an ASCII keyboard. I have > > programmed > > an old AIM-65 to be a keyboard, but I'd rather get a dedicated keyboard. > > Are there > > any ASCII kbds around anymore? Is it possible to use some circuit to > > convert the > > output of a PC kbd to ASCII? > > > > Any ideas? > > > > river FWIW, seeing this reminded me I've got some old RCA COSMAC boards here. Does they qualify as "old microprocessors?" ###### Message-ID: <36DB28CB.8629F8D6@flash.net> From: Richard Lamb Reply-To: lamb01@flash.net Organization: Earth X-Sender: "Richard Lamb" (Unverified) X-Mailer: Mozilla 4.04 [en]C-FLASHNET (Win95; I) MIME-Version: 1.0 Newsgroups: alt.folklore.computers Subject: Re: Old Microprocessors References: <01be5e4a$ef9590e0$8512083d@Lockheed> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 31 Date: Mon, 01 Mar 1999 23:45:24 GMT NNTP-Posting-Host: 209.30.91.56 X-Complaints-To: abuse@flash.net X-Trace: news.flash.net 920331924 209.30.91.56 (Mon, 01 Mar 1999 17:45:24 CDT) NNTP-Posting-Date: Mon, 01 Mar 1999 17:45:24 CDT Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!newscore.univie.ac.at!news-spur1.maxwell.syr.edu!news.maxwell.syr.edu!nntp.flash.net!news.flash.net!not-for-mail I'd like to have one of those old AIM-65's! Add one to my little collection... Anybody wanna part with one? email lamb01@flash.net Richard Lamb river wrote: > > Hi, > > How do I convert 20mA current-loop to RS232C? I got an old SC/MP and > old 2650 SBCs that I'd like to fire up. > > Also, I got another 2650 system that needs an ASCII keyboard. I have > programmed > an old AIM-65 to be a keyboard, but I'd rather get a dedicated keyboard. > Are there > any ASCII kbds around anymore? Is it possible to use some circuit to > convert the > output of a PC kbd to ASCII? > > Any ideas? > > river ###### Message-ID: <36DB292A.FDE31A69@flash.net> From: Richard Lamb Reply-To: lamb01@flash.net Organization: Earth X-Sender: "Richard Lamb" (Unverified) X-Mailer: Mozilla 4.04 [en]C-FLASHNET (Win95; I) MIME-Version: 1.0 Newsgroups: alt.folklore.computers Subject: Re: Old Microprocessors References: <01be5e4a$ef9590e0$8512083d@Lockheed> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 27 Date: Mon, 01 Mar 1999 23:46:58 GMT NNTP-Posting-Host: 209.30.91.56 X-Complaints-To: abuse@flash.net X-Trace: news.flash.net 920332018 209.30.91.56 (Mon, 01 Mar 1999 17:46:58 CDT) NNTP-Posting-Date: Mon, 01 Mar 1999 17:46:58 CDT Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!isdnet!sunqbc.risq.qc.ca!nntp.flash.net!news.flash.net!not-for-mail Hey River, I believe there is a circuit shown in the SYM-1 Apps manual. I don't have it here, but if you can find one... It's just a single transistor and a couple of r's and c's. river wrote: > > Hi, > > How do I convert 20mA current-loop to RS232C? I got an old SC/MP and > old 2650 SBCs that I'd like to fire up. > > Also, I got another 2650 system that needs an ASCII keyboard. I have > programmed > an old AIM-65 to be a keyboard, but I'd rather get a dedicated keyboard. > Are there > any ASCII kbds around anymore? Is it possible to use some circuit to > convert the > output of a PC kbd to ASCII? > > Any ideas? > > river ###### Newsgroups: alt.folklore.computers Subject: Re: Old Microprocessors References: <01be5e4a$ef9590e0$8512083d@Lockheed> <36DB28CB.8629F8D6@flash.net> <36DB5BF8.6041@prodigy.net> X-Newsreader: NN version 6.5.1 (NOV) From: jasnider@shell1.iglou.com (Jill A. Snider) NNTP-Posting-Host: 192.107.41.17 X-NNTP-Posting-Host: 192.107.41.17 Message-ID: <36dee6ca.0@news.iglou.com> Date: 4 Mar 1999 15:02:18 -0500 X-Trace: 4 Mar 1999 15:02:18 -0500, 192.107.41.17 Lines: 30 X-NNTP-Posting-Host: news-incoming.iglou.com Organization: IgLou Internet Services, Inc. Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!news.bme.hu!news.iif.hu!newscore.univie.ac.at!howland.erols.net!newspeer.monmouth.com!rill.news.pipex.net!pipex!ams.uu.net!ffx.uu.net!in4.uu.net!news.iglou.com!shell1!jasnider >> river wrote: >> > >> > Hi, >> > >> > How do I convert 20mA current-loop to RS232C? I got an old SC/MP and >> > old 2650 SBCs that I'd like to fire up. >> > >> > Also, I got another 2650 system that needs an ASCII keyboard. I have >> > programmed >> > an old AIM-65 to be a keyboard, but I'd rather get a dedicated keyboard. >> > Are there >> > any ASCII kbds around anymore? Is it possible to use some circuit to >> > convert the >> > output of a PC kbd to ASCII? >> > >> > Any ideas? >> > >> > river As to the ASCII keyboard, it seems to me that it should be a fairly trivial task to emulate an RS-232 ASCII keyboard with almost any computer with a serial connection and BASIC. Oh, wait, this is a board that's even older than my ELF II, which used a 3-wire RS-232 connection to the ASCII keyboard, so maybe it's not even that sophisticated? -- Pat Larkin First initial Last name at iglou.com -- ###### From: gleason@mwk.com (Lee K. Gleason) Newsgroups: alt.folklore.computers Subject: Re: Old Microprocessors Message-ID: Date: 4 Mar 99 15:34:59 CST References: <01be5e4a$ef9590e0$8512083d@Lockheed> <36dee6ca.0@news.iglou.com> Reply-To: gleason at mwk.com Organization: Control-G Consultants Lines: 27 Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!news-ge.switch.ch!newscore.univie.ac.at!howland.erols.net!newsfeed.cwix.com!4.1.16.34!cpk-news-hub1.bbnplanet.com!atl-news-feed1.bbnplanet.com!news.gtei.net!mwk!gleason >>> > >>> > How do I convert 20mA current-loop to RS232C? I got an old SC/MP and >>> > old 2650 SBCs that I'd like to fire up. >>> > >>> > Also, I got another 2650 system that needs an ASCII keyboard. I have >>> > programmed >>> > an old AIM-65 to be a keyboard, but I'd rather get a dedicated keyboard. >>> > Are there >>> > any ASCII kbds around anymore? Is it possible to use some circuit to >>> > convert the >>> > output of a PC kbd to ASCII? >>> > On old systems I have that use current loop, I use a little circuit I found in an Intel data book. It basically "steals" the negative voltage from the rs-232 device it's talking to, and stores it in a capacitor, then uses it when it needs to go below zero volts on its leads. Has a transistor, a cap, a resistor or two. Simple. Works good...it works as long as you don't want top connect two devices that use this trick together...as a matter of fact, it's what I use on my AIM-65 to convert it's 20 MA to RS-232. If you don't find a better solution, let me know, and I'ls send you a copy... Lee K. Gleason N5ZMR Control-G Consultants gleason@mwk.com