Hi Tony Thanks for the reply. I looked at the circuit use on the SA801. It looks relatively simple. It has the divider for creating other sector counts out but all I need is the one shot circuits. It used 9602s but I'll most likely use some 555s or a 556. The SA801 used feedback on the 9602 to keep them from being retriggered. My board was intended to be used with 5.25 disk drives but looking at the ribbon connector, it was wired for an 8 inch drive. It is a 40 pin connector but has signals with the same spacing as would be on a 50 pin ( 50 pin number minus 10 ). This leads me to think they had an interface board to translate the pins and generate the sector pulses. It might be that they had their own hard sectored 5.25 drive made with the 40 pin connector but I doubt it. I have a pile of 5.25 disk that are double density but also are hard sectored. It is possible that the disk are really just softsectored format but I rather doubt that since I have more than 50 such disk. From what I was told, Polymorphic only used hard sectored for every thing. The firmware code I have is intended for a 10 sectored disk but it looks like the variables for timing and sector count can be overwritten. I do have some 8 inch disk( 5 ) that are SSSD hard sectored as well. These would have the same data rate as the double density 5.25 disk but have 32 sector holes. The firmware is definitely 10 sectored. I think I have most every thing that is on the 8 inch disk on the 5.25 inch disk, from the lables on the disk. Still, setting up for 8 inch drives is a future project. The serial chip used is one of the fancier ones that has the CRC16 built in. The single density controller that I have in my Polymorphic 8813 uses a simpler serial chip. I've been disassembling the code but still haven't figured out how they get it to read the disk. I've found the code that does the read but I've not been able to back track it to the command interpreter. I suspect that the read code was one of the pieces set by the firmware on the main system bus. The board has two memory windows on the S-100 side. One is from 1000H-2000H while the other is a 16 byte window for parameters and command handshake. One of the commands goes to code that would be loaded into this shared memory window. These disk are of great archival value. They are the backup disk for the code that Polymorphic sold. It even includes source code for the version of BASIC that Polymorphic wrote. I've already read the single density disk but still need to get these double density ones read. I don't have the right system firmware for this board so I'm doing a lot of reverse engineering. I'm actually expecting to run this on my Poly88 instead of the 8813. I'm more familiar with writing code for the Poly88 but it is a cassette based system. The controller board is a Z80 and the Poly88 is a 8080 but I think there are enough routines on the controller boards firmware that I can assemble 8080 code on the Poly88 for the code that I'd load into the common area of the two busses. I'll just call the routines in the controllers firmaware. Dwight _________________________________________________________________ Don't get caught with egg on your face. Play Chicktionary! http://club.live.com/chicktionary.aspx?icid=chick_wlhmtextlink1_dec