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What to do with a 68 K-based CPU board used in the 1990' for piloting a bank of modems.

jplr

Experienced Member
Joined
Sep 3, 2022
Messages
139
Location
Brittany/France
Hi, when I changed of job in the 1990' I kept a 68K VME board that must have been used to drive a bank of V23 modems. If I remember correctly they were used to communicate with Minitels, the French videotext.
At that time I intended to use it to build later a computer with it. I had in that job already familiarity with VME hardware (SGTD for those in my field) and microprocessor boards in general.
Now I am 30 years older, retired and wonder what to do with that board. I forgot completely what I knew about 68K VME boards. The memory connector is rusty but it could be replaced. Could it be used as a SBC?
Does someone have some idea or pointers to resources to make a SBC from this board?
 

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cruff

Experienced Member
Joined
Dec 12, 2012
Messages
395
Location
Colorado
Looks like there isn't much on that board other than some serial chips, a RTC, RAM, ROMs and the CPU. It must have acted as a serial line peripheral controller for another computer, so the resources to use it directly as a SBC will be limited to that set of features. You'll have to reverse engineer the address space assignments of everything so you would know how to writer your own software for it.
 

daver2

10k Member
Joined
Jun 19, 2012
Messages
14,349
Location
UK - Worcester
It'll be fun :)!

I am looking to convert a DEC terminal server into an SBC. Fortunately, the documentation is available on bitsavers. This is a 68K board with 8 serial ports, DRAM, EPROM and various other peripheral chips. Interestingly, there is no hardware refresh for the DRAM. It is implemented in software via a timer interrupt. This is 'novel' because the timer interrupt vector is in DRAM and we use that to vector to the handler to refresh the DRAM. As I said, fun!

The MEX68KECB (http://www.easy68k.com/paulrsm/mecb/mecb.htm) contains a very nice little monitor called TUTOR. The sources are available for this.

Yes, the fun will be in ascertaining the memory map(s) for your specific card.

Dave
 

jplr

Experienced Member
Joined
Sep 3, 2022
Messages
139
Location
Brittany/France
Thanks for all answers, I guess the easier would be to dump the ROMs. Is there some modern tool to do that?
Or maybe connect a console to the DB25 and see if there is a monitor?
Is there some quick and dirty way to simulate the VME bus power supply signals?
 

Bruce Tomlin

Experienced Member
Joined
Jan 6, 2010
Messages
303
Location
San Antonio, TX
As an SBC, you could do worse than have four serial ports, I think that would be a good start.

Yes, dump the roms, a disassembly should give plenty of info about the address layout. Pop them out and read them with an average EPROM programmer. Then zip up the files. With my disassembler, it will be a fun couple of hours for me to make a passable disassembly, ha ha. It looks like 384K (6x27512), so it will be interesting to see exactly what is in there.
 

Plasmo

Experienced Member
Joined
Aug 29, 2017
Messages
208
Location
New Mexico, USA
I have reverse engineered a 68K board and ported CPM/68K to it. CPM/68K needs only one serial port and you can put a small ROM disk in 384K EPROM.
 

wrm

Member
Joined
Sep 15, 2013
Messages
33
Location
Cape Town, South Africa
I would definitely make an SBC out of that. Looks to have everything you need. Sure, dump the ROMs, but for starters hook up the serial ports one by one and see what comes out.

From what I remember one needs to do at least some termination on the VME bus for a board to come up, I have schematics... somewhere. In some format. But info should be available on the 'net. Lemme know if you need help there. Or if you decide it's too much hassle and you need a new home for it :)
 

jplr

Experienced Member
Joined
Sep 3, 2022
Messages
139
Location
Brittany/France
> Or if you decide it's too much hassle and you need a new home for it :)

Thanks for the offer, it may be the wiser solution.
I noticed you are in South Africa. The French postal service website says it would cost 45,20 € for 2kg and there is some paperwork, I will have to gather more information about that. I estimate also to have maybe 5 or 10 euros costs for packaging.
 

wrm

Member
Joined
Sep 15, 2013
Messages
33
Location
Cape Town, South Africa
> Or if you decide it's too much hassle and you need a new home for it :)

Thanks for the offer, it may be the wiser solution.
I noticed you are in South Africa. The French postal service website says it would cost 45,20 € for 2kg and there is some paperwork, I will have to gather more information about that. I estimate also to have maybe 5 or 10 euros costs for packaging.
I hang out in Slovenia too so can provide address there.
 
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