XEROX ALTO - DIABLO DISK TOOL CREATION
I figured out the root cause, which was a timing issue in when I latched in the contents read out of RAM. The last data written was still on the bus until the RAM completed its access cycle, giving me data in transition but not yet fully representing the memory content.
I had another spot with a similar timing issue, so that I was returning the 'prior' version of a byte not the one being retrieved. Those got corrected and I was successfully retrieving the RAM contents to files.
Now I need to schedule time on the real Diablo drive to upload the contents of a couple of disk cartridges, checking them carefully to be sure I am properly capturing content. Once that is good, I can grab the contents of all four cartridges in our possession now and eventually the others from PARC.