8257 use in Intel MDS IOC

F.Ulivi wrote: That's actually my IOC board. I hadn't noticed that it has an 8237A! Amazing. Thanks for pointing that out. That's definitely proof that the code can work with the 8237A, now I need to scrounge an 8257 and determine whether the board w/ the 8237A rework will still work with the 8257. IIRC, the 8237A had some improvements over AMD's original 8237 design, so it's possible that a non-A 8237 might not work. I haven't compared the A and non-A datasheets yet. I've been making progress on reverse-engineering the IOC firmware. They wrote it as four separate 2K ROMs, each of which has a table of fixed entry point addresses for entry from the other ROMs. (The first ROM has the entry points interleaved with the RST n vectors.) The first ROM is startup and diagnostics, and the second is the command handler and the driver for the intergral single-density floppy. I haven't yet started on the third and fourth. There are a few input and output bits they access that are not used in the normal IOC, but perhaps are used in the IOC-III used in later Series III machines. In the RAM test, if the back panel mode switch is set to diagnostic mode, they insert a delay (which I haven't timed) between the write and verify passes of the diagnostic, presumably to test whether memory refresh is working. I was hoping that the floppy driver had support for two drives, but as far as I can tell so far, it does not. I could be wrong since I haven't puzzled out all of the details yet. My IPB is the old version (1001194) without the 20-bit addressing daughterboard (1002234). I don't have a schematic of the daugherboard, but all it does is use a 74LS30 and a resistor pack to pull up the A10/ through A13/ address lines on the Multibus, and disable the on-board RAM address decode if they aren't all high, in order to prevent the board from incorrectly responding to RAM addresses from 0x10000 through 0x17fff, 0x20000 through 0x27fff, etc. I can easily hack that in myself. I'd really like to replace the IPB with the 8085-based IPC, if anyone has a spare available. Also looking for an RPA, RPB, or RPC 8086 board to effectively turn it into a Series III, and the two-board double-density floppy controller. (This Series II was previously equipped with the double-density controller, as the I/O cabling is still present.) Also it would be nice if anyone has a later rev of the Series III schematics. The set that Al has kindly provided on Bitsavers is 121642-001A, which appears to be the earliest set Intel printed, and doesn't cover the RPB or RPC, or the IOC-III.