Tks Dean, Not yet ruled out a silly mistake (so thanks for the tips, double check it again)... but... as you saw on my previous post it looks like this is a peculiarity of this PC the south bridge or whatever as on others it seems to work fine. tks, for the book reference ;-) will look for it.
lc. Dean Weiten wrote: > 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. > _______________________________________________ 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.