Flex Disc options for the HP 9825

[Paul Berger]

Some time ago there was a discussion about the elusive 98228A ROM that 
supports both the 9885 and 9895 diskette drive units on a 9825T, well 
good news!  A fellow MoHPC member David Ramsey very kindly loaned me 
his, and with a little careful reading of the service manual along with 
studying Tony Duell's schematic I got a good idea of how it work, and 
observing the memory bus using a logic analyzer confirmed how it 
worked.  I was able to dump the ROM using GPIO cards in a 9920 to 
simulate the memory bus, I actually went on and dumped all the ROMs in 
the 9825T as well as a couple other I had.  I have successfully created 
a clone of the ROM and have even fit it into a a ROM shell.  I am going 
to try creating a PCB for it too, what I have now is just hand wired, 
but it works.  In the end the ROM module did not turn out to be very 
complicated.  I am just in the process of documenting my project and 
will release a package soon with full documentation and most importantly 
the ROM image.  I plan to donate my package along with all of my ROM 
images to hpmuseum.net.

Paul.