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Polar Instruments DDT Disk drive tester - Firmware needed !
pedrocelli:
Since many years I'm using a Polar DDT Disk drive tester for function test of 3.5, 5 1/4 and 8 inch floppy disk drives.
The tester was made about 1989 by Polar Instruments Ltd (founder Doug Campbell).
The tester has become unreliable during startup, as it shows a checksum error, and occasionally it does not startup at all. Sometimes it works. Checking the internal ROMs showed, that bits of the firmware are not stable, others may have changed already.
I would like to program a new ROM, but need a working firmware file for it.
Attached a picture of the unit and the current dump of the firmware. The software version is V2.2 on a 32kB Eprom.
In first place, I've contacted Polar customer service, which have kindly responded, but no firmware or a device could be found anymore.
So, my hope is, that someone else owns this unit and could make a copy of the standard 32k internal Eprom.
aeg:
Maybe try reading the ROM at reduced Vcc. This lowers the threshold, so it might make the flaky bits read OK.
pedrocelli:
My initial attempt was to heat up the Eprom during the read operation of the prommer. A few bits changed and it seems to better match to the disassembly program flow. But burning this data into a new Eprom didn`t let to a working system.
As you suggested, I lowered VCC of the Eprom by 0,3 and 0,6 volt, but unfortunately in both cases, the binary data just became more flaky during every read operation and reduced VCC. In my opinion, VCC variation does not compensate the data degradation.
Hopefully someone else owns a POLAR DDT to get the problem solved.
aeg:
It looks like the loop at 1675 to 1697 calculates the ROM checksum by mod-256 addition and the code at 169a wants the sum to be zero. But the sum of POLAR_DDT.bin is 254. It could just be one flipped bit in the second LSB position? (Or it could be 254 flipped bits...)
If it reads worse at reduced Vcc, maybe it would read better at increased Vcc? Normally it should read worse at increased Vcc, but maybe some extra charge ended up on unprogrammed bits, rather than charge leaking from programmed bits.
pedrocelli:
Your analysis on the checksum routine is very helpful. I simulated the routine and it ends up with 254, as you mentioned.
The POLAR_DDT.bin file already had some corrections, based on the temperature treatment and Disassembly (see in the attached text file)
Based on these corrections, it is fair to say, that Eprom values flip on bit zero and on uneven addresses. Therefore address 0009 might be another good candidate and just one bit left ;-)
Including all corrections in a new Eprom, the tester only gets to the boot prompt and stops at "P" of "POLAR DDT". That is strange but could be an indicator, where during the startup phase, the program gets stuck.
The mentioned increase of VCC, I have done during the VCC reduction test. Up to 6V, there was no difference compared to 5V nominal.
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