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I'm fascinated by the little 3-chip(+) designs of the late 70's and early 80's that used a 6532 for 128 bytes of RAM plus I/O (like the Beta, CEPAC-6502, and EMUF-6504).

Last year I read about the John Bell Engineering "82-300" board which is the simplest design with a 6532 chip that I've seen so far. It uses an RC oscillator and the active components are a 6502, a 6532, a 2716 (2K) or 2532 (4K) EPROM, and a transistor. I haven't found a Manual yet but someone was kind enough to send me a copy of the hand drawn schematic that accompanied the 82-300 board kit. I've attached my interpretation of that schematic for anyone who may be interested.

Cheerful regards, Mike, K8LH

It's hard to find anything about the boards from John Bell Engineering. Some months ago I was looking for anything concerning to the AD converter. I remembered my board which I bought in 1990 from a dealer in Karlsruhe, West-Germany, who sold empty boards from Taiwan:



I just found this web site after searching for years. With this picture it was easy for me to buy the missing chip and heat the solder iron:



Look at the letters written on the original board and the Taiwan board! Funny taiwanese people

Regards, Ralf

Hi Michael,

this is the CEPAC-6502 you mentioned. I call this thing SYMilar as it consist of a NMOS 6502, 6532, RAM, and ROM (but no 6522s) similar to the SYM-1.
It uses bit banging for serial I/O (like the SYM). And the monitor program is very similar to the SUPERMON. I added the RAM and the TTL<=>RS232 converter and used a 74LS138 (with 3 diodes forming an AND gate!!) to override the memory map. Now there is 24K (3x 8K) RAM, then 8K I/O (= 32x the 6532), and 32K ROM (last burned April 1996). The RAM, decoder, and RS232-level translator are built on a perfboard. There I used a wire pencil to connect the RAM to the VG-connector. This sort of wire is very thin and coated with a tough isolation that only melts away when soldered. This is a quick and dirty way of building a circuit and a very nasty one if you need to change something In that time I managed to disassemble SYM-Basic V1.1 so far that I could transfer it to this board. Currently it is heavily computing prime gaps

Once I found the article to this board once published in the German monthly c't somewhere (bitsavers?) but I saved a PDF (sorry only German). Cheers.

edit(1):
+ There is a bug in the schematic around the 74xx74 dual-FFs. Michael post below shows the corrected version!
+ I used a 74LS139 (not 138 as stated above) to generate a /CS (via 3 diodes wired AND) with one half LS139 and a qualified /WE with the other half.

I like it!

Very nice CEPAC-6502 expansion.

Please note there was an errata published in a later c't issue about an error in the schematic around the 74xx74 in the clock circuit. I edited the schematic to include the correction (below).

Cheerful regards, Mike, K8LH

Thank you, Mike!

I edited my post to point to the corrected schematic.

Someone was kind enough to send me a copy of the documentation that came with the John Bell Engineering 82-300 board (attached below).

Cheerful regards, Mike, K8LH

<added>

wrong board manual. my apologies. I'm still lookin' for an 82-300 manual...

Thanks Michael!

I had this 80-153 manual already several years on my John Bell page. I did add this spring some advertisements by John Bell, a large catalogue of small boards!

http://retro.hansotten.nl/6502-sbc/john ... ring-sbcs/

Hi Dallas:

Thank you for sharing those documents. I would love to see some pictures of your systems.

In the early 80's I wrote the firmware for the EPG (Electronic Program Guide), a 6502 based 'character generator' which was installed in the 'head end' at cable companies around the country. TV listing data was sent via land-line to an uplink near Chicago where it was inserted into one of the horizontal scan lines within the vertical blanking interval of the WGN signal (youtube video).

Take care. Cheerful regards, Mike, K8LH

In the early eighties I would have drooled over that catalogue; I was using the Tangerine Microtan 65 and designing essentially similar circuits at the time.

Curious that they didn't offer any sort of power supply (and I don't recall in the 84 catalogue seeing even a voltage/current spec for the cards, though I don't notice regulators on board so I assume 5v).

Neil