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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 20th Nov 2022, 10:08 pm   #1
ortek_service
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Default Infotron TL78-02-29 (PN 170152) 26KB Computer (6502A) Board

An unusual '6502A Computer Board', I picked-up (for 10p!), at a Radio Rally > 20yrs ago, that I've recently rediscovered and I thought may be of interest - or even someone may recognise? (See attached Pictures / zip file containing full-size ones)

I can't really find any info on the 'net about this, but have found that Infotron made (as well as the odd 6502 In Circuit Emulator?) Serial Data Comms Test Equipment - So it's most likely a board from out of one of these.
- Especially as I have dumped all the PROM's (contents attached), and found 'PRESTEL' (+ Password) and various Serial Data terminology words in these. (Plus what appear to be the reset / Interrupt vectors at the end of one)

The '26K' actually seems to be 16K RAM (8off 4116) + 10K PROM (20off 512x8bit PROM's). There are actually only 17off of these installed, but the 3off pairs of 10way SIL flush-mount pin-socket strips used still have their silicone sealant intact so have never had any installed.

This board must have cost quite a bit to make, as it's 4-layer (not very common back in <=1980, when it was probably designed - judging by what most IC's are date-coded). And especially as they chose to use 17/20off PROM's, which surely must have cost more than a few EPROM's back then (Although I have seen even 2708's at prices 10 - 30 each in adverts around then, but I imagine these PROM's weren't much cheaper each / cost more in total for equivalent capacity). It would also be more costly to make any firmware changes, as at least you could reuse EPROM's.

These programmed PROM's have been numbered 010x to 200x, where the first two digits are the position on the board / memory map. And last two numbers seem to be a revision number (A little strange that ere seems to be a fairly random variation across the ROM space, as I'd expect anything other than a very minor change to the firmware, to result in most memory locations from change to top of ROM space to need to alter). As well as a variety of ways of marking these, they've also used multiple types: SN74S472N & MMI 5349-1J

All other IC's are 74LS logic (quite a lot of) and four N8T26AN Bus-transceivers. Plus there's a 12MHz Xtal oscillator, that must have got divided down to <=2MHz for the 6502A / fed externally via the two 50way dual-row 0.1" headers for all I/O & power to board - Which I guess must have connected to some ACIA / UART's on another board I'm missing.

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Old 21st Nov 2022, 12:01 pm   #2
Pernod70
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Default Re: Infotron TL78-02-29 (PN 170152) 26KB Computer (6502A) Board

I created a simple machine with the ROMs in MAME:
RAM: 0x0000-0x3FFF
ROM: 0xD800-0xFFFF (0xDA00-0xDFFF is empty ROM sockets)

When running it tries to setup some unknown IO at 0x9000-0x9007, maybe serial port(s), one of which is likely expecting a terminal, but I didn't recognise the data being sent to determine the type of ACIA/UART device at these addresses.

If I force it through this initial setup then it'll continue to enable interrupts and happily loop waiting for something to happen.

As there's text in the ROM I was hoping to maybe see it write something to video RAM so that I could get it to display something, but looking more likely that it's writing anything to be displayed via serial to a terminal.
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Old 22nd Nov 2022, 2:37 am   #3
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Default Re: Infotron TL78-02-29 (PN 170152) 26KB Computer (6502A) Board

Thanks for doing that - I hadn't thought of actually trying to run it on a simulator, only maybe disassembling it, to see what it was doing.

As there's no video controller IC's on it and it doesn't look like they've used any of the logic to generate a video signal, then unless they put a CRTC on another board, I suspect it's all serial data in & out and maybe to two 50way headers are wired the same, with each going to an ACIA/UART IC.
Unfortunately there's no labelling of the connectors, as to what they connect to.
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