TMS7000 dumper rev. B sneak peek and obscure footprint processor dumping

Do not use git branches, this is a way to lose shit you’ve been working on. Do not use git stashes, this is a way to lose shit you’ve been working on *and it’s not backed up anywhere*. Git is just too complicated to use all of it and expect to not lose stuff. I’m trying to get back into this project after an entire year and figuring out where we left off and what was going wrong has been a whole ordeal.

This is the resumption of a project on dumping the internal contents of the tms7000 processor. Over a year ago we had moved on from the hardware SPI implementation of the revision A to the parallel approach of revision B. I don’t recall why we moved to a parallel interface, but I think it had to do with one of the pincount reduced chips not being compatible with our original SPI method. I think the later bigger chips are also not compatible with SPI though, so I’ll update this when I find out. The board with no revision had no ability to detect CMOS/NMOS and had a different resistor value for the LED. Revision A added those, and revision B changed from SPI to parallel.

In the interim since the last update we have been designing adapters for a whole new series of chips. The 7xx8 chips. These are bigger pincount chips that seem to be one of the last sort of tms7000 around. They look like they were more popular in europe and that’s where we found this databook. This is a 1991 version of the tms7000 databook and it’s not scanned or on bitsavers yet. I’d like to do that at some point, but for now I took pictures of the most interesting sections and they are up on my github.

The board was designed specifically to work with the DIP40 variant of the tms7000 but we now have adapters to successfully dump the:

• DIP 28 0.07″ pitch
• DIP 40 0.07″ pitch
• DIP 64 0.07″ pitch
• DIP 64
• PLCC 44
• PLCC 68
• QFP 64

Today’s PCBWay sponsored board is this nice QFP64 adapter. It worked first try because the chip inside is basically the same as everything else, I just used the new databook to connect the dots. I got this one in a stylish yellow. I think it looks just as good as yesterday’s red, but in an unexpected way. This is one that you might think at first glance is a flex PCB, but it’s not.

There is a problem with the tms7000 dumpers we have though. rev.A only works on the 40 pin, and 44 pin chips. rev.B theoretically works on all of them, but it has issues locking up on certain 40 pin chips though. We’re not 100% sure why, but it may have to do with the fact we’re clocking the chip and we don’t do it fast enough to keep the memory alive in certain ones. So we have this conundrum, all* chips can be dumped, but not with one universal dumper. This is a problem we’re actively working on and hope to get it solved soon. We have a lot of chips purchased from ebay and dumps of them all up on github so we can test until they all work. An interesting aspect about this project is they all have internal rom. Ignore the part number printed on the chip, they all have some sort of mask rom. We have even found some that we think are factory test roms and are loaded in multiple different package chips we got from different sources. Others may be rejects that TI re-labeled to sell as external-only versions, but they still sent them out the door with code in them. If you have truly done everything, and I mean everything else important in life and you need some sort of project… feel free to start disassembling this code discovered in NOS chips from ebay.

The asterisk in the last paragraph is for another couple chips, the QFP60 and the 54 pin 0.07″ pitch DIP, those have a different pinout and addressing modes that we don’t have a databook for. I took a stab at guessing some of it, but apparently I guessed wrong and they didn’t work. I have an upcoming entry talking about the plans to dump those.

This is another project not up for purchase because really, no one needs these. Well, maybe one person a decade, but I’m happy to mail them my 4 spare boards when that comes up. The dumper itself might go up there but not until it’s fixed.