Luis, As have many others, I've stubbed my toes on ISA interfacing lots of times. The best reference on the subject is "Interfacing to the IBM (r) Personal Computer", by Lewis C. Egeebrecht, from Sams. It's old and may be out of print, but it's an essential resource for anybody dealing with 8 or 16-bit ISA. You will have to ignore the sections in PS/2 Micro Channel architecture of course :-) There are a few typos (e.g chapter 10 - description of SBHE - SBHE should be inverted, and /SBHE=0 A0=1 is odd byte 8 bit transfer not "invalid") but it is an *excellent* reference.
Back to your problem. 8 bit I/O should work if you are decoding the lower 16 bits of address (NB **only** 16 bits) qualified by AEN low and using /IOW & /IOR to strobe. One common error that I've made a few times is to ignore the AEN, which typically works but messes up the DMA so that floppy drive access fails. Be sure to leave I/O Channel Ready alone unless you want to extend the I/O cycle time; and then only drive it low when your device is accessed. To enable 16 bit I/O, you drive I/O CS 16 low when you have valid address to your board (address & AEN, no need for strobe), then you must do an 8 bit or a 16 bit cycle in accordance with A0 & /SBHE. This because the X86 instruction set allows for 8 and 16 bit I/O, and you don't know which one you will be seeing when you get selected. That should be all there is to it. All this with the caveat of course that free advice is worth... well, you know :-) Regards, Dean Weiten dmw -at- weiten.com _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
