From: "George Gonzalez" Newsgroups: alt.folklore.computers Subject: Weird PCM-12 front panel Lines: 38 X-Priority: 3 X-MSMail-Priority: Normal X-Newsreader: Microsoft Outlook Express 5.50.4133.2400 X-MimeOLE: Produced By Microsoft MimeOLE V5.50.4133.2400 Message-ID: Date: Thu, 07 Sep 2000 15:23:21 GMT NNTP-Posting-Host: 38.27.198.225 X-Complaints-To: abuse@flash.net X-Trace: news.flash.net 968340201 38.27.198.225 (Thu, 07 Sep 2000 10:23:21 CDT) NNTP-Posting-Date: Thu, 07 Sep 2000 10:23:21 CDT Organization: FlashNet Communications, http://www.flash.net Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!newsfeed-zh.ip-plus.net!news.ip-plus.net!news.tesion.net!news.belwue.de!informatik.tu-muenchen.de!fu-berlin.de!nntp.flash.net!news.flash.net!not-for-mail Xref: chonsp.franklin.ch alt.folklore.computers:63251 Way back when Intersil came out with a PDP-8 on-a-chip, the 6100 IIRC. One small company, oh what was it? made a PCM-12, which was a cheap PDP-8 built around this chip. My department back then bought two of these in kit form. It wasnt exactly a Heathkit, but we did eventually get the kits working. I did spend many hours debugging the 4K memory boards. One had several intermittent chip sockets, and I'd run the DEC core memory test tape (which probably was far from optimum for debugging MOS memory), while carefully tapping each memory chip. I'd be carefully tapping each chip with a screwdriver handle-- when I heard the TTY pound out a line of error info, I know I'd found the right socket (or near it anyway). A lot of work to get another 4K going! Anyway, the CPU chip as you might expect did not have the 72-odd pins you'd need to feed all the traditional panel display lights, so the chip had a WEIRD virtual front panel refresh interrupt mode, which was a lot like a periodic interrupt routine, except it had lots of really bizarre conventions. The only one I can recall is that every path thru the front panel servicing routine had to be an even number of instructions long for some long-forgotten reason. Anybody remember any details about this? It was the strangest hardware/software kludge I've ever seen. -- George ###### Message-ID: <39BAA679.E08BA32@bellatlantic.net> From: hg/jb Reply-To: shsrms@bellatlantic.net Organization: The Keltic League X-Mailer: Mozilla 4.73 [en]C-CCK-MCD BA45DSL (WinNT; U) X-Accept-Language: en MIME-Version: 1.0 Newsgroups: alt.folklore.computers Subject: Re: Weird PCM-12 front panel References: Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 44 Date: Sat, 09 Sep 2000 21:06:35 GMT NNTP-Posting-Host: 138.88.34.164 X-Complaints-To: newsadmin@bellatlantic.net X-Trace: typhoon1.ba-dsg.net 968533595 138.88.34.164 (Sat, 09 Sep 2000 17:06:35 EDT) NNTP-Posting-Date: Sat, 09 Sep 2000 17:06:35 EDT Path: chonsp.franklin.ch!pfaff.ethz.ch!news-zh.switch.ch!newsfeed-zh.ip-plus.net!news.ip-plus.net!news.tesion.net!news.belwue.de!news.uni-stuttgart.de!uni-erlangen.de!newsfeeds.belnet.be!news.belnet.be!xfer13.netnews.com!netnews.com!europa.netcrusader.net!199.45.45.8!cyclone1.ba-dsg.net!typhoon1.ba-dsg.net.POSTED!not-for-mail Xref: chonsp.franklin.ch alt.folklore.computers:63584 the 6100 had a special memory path for the front panel code. The 6120 had capability for two 32KW banks, one for mem, one for frontpanel/console panel. It was certainly not your average PDP8 or PDP12 panel! bob George Gonzalez wrote: > > Way back when Intersil came out with a PDP-8 on-a-chip, the 6100 IIRC. > > One small company, oh what was it? made a PCM-12, which was a cheap PDP-8 > built around this chip. > > My department back then bought two of these in kit form. It wasnt exactly a > Heathkit, > but we did eventually get the kits working. I did spend many hours > debugging the 4K > memory boards. One had several intermittent chip sockets, and I'd run the > DEC > core memory test tape (which probably was far from optimum for debugging MOS > memory), while carefully tapping each memory chip. I'd be carefully tapping > each chip > with a screwdriver handle-- when I heard the TTY pound out > a line of error info, I know I'd found the right socket (or near it anyway). > A lot of work > to get another 4K going! > > Anyway, the CPU chip as you might expect did not have the 72-odd pins you'd > need to > feed all the traditional panel display lights, so the chip had a WEIRD > virtual front panel > refresh interrupt mode, which was a lot like a periodic interrupt routine, > except it had lots of really > bizarre conventions. The only one I can recall is that every path thru the > front panel servicing routine had to be an even number of instructions long > for > some long-forgotten reason. > > Anybody remember any details about this? It was the strangest > hardware/software > kludge I've ever seen. > > -- George