Troubleshooting self-test Error 57

[pintoguy]

Oh thanks James for your thorough post. I have a few comments and answers

Having established that the FDC RAM seems to work ok by your previous tests, we can be semi-confident that the values you wrote went into the FDC RAM

mmm, I must be too much of a HDD guy thinking that you could have faulty memory location in a RAM chip, and perfectly good ones at the same time on the same chip. So, writing OK at $FCC017 implies that you will write OK at $FCC001 ? As I told you, I write and read back OK at $FCC017, but can only write up to $7F at $FCC001. Past $80, I always read back 00

The FDC code will zero the command byte (that you wrote to FCC001) when it executes the command.

Even after I write in service mode, and read straight back ?

In any case, good work finding the FDC code listing and working through it!

Thanks !

AFAIK, the only listings available are for the 400K versions of the 3.5" drive version of the I/O Board ROM

Yes, that's the one I saw on bitsavers

When error 57 occurs, are both FCC017 and FCC011 returning 01?

No, FCC011 returns 00