Hi,
I have a PC104 from kontron (mops_lcd) that I can't read IO ports from the ISA bus, The write to ports is ok but the read gets
0xff always. (even with datalines forced '0' all the time) Looks that IO input is comming from elsewhere as onboard devices like LPT or COM work well I suspect a bridge config or whatever... Kontron support doesn't really help and I wonder if anyone has stepped into this before...Luis C.
There's probably a buffer somewhere that has to be enabled to let the PC104 data lines drive the processor local bus (which may very well be address/data multiplexed) at the appropriate time during a read cycle. While writes can be broadcast to multiple bus branches, reads can only have one such buffer enabled and whatever logic is supposed to do that probably hasn't been told that this address means a read from this bus.
The fact that you can short the data lines to ground without crashing the system also points to your PC104 bus being somewhat isolated from the main processor bus.
And remember the different control signals for IO vs memory access.
Thanks, I suspect indeed of a bug on the isa-bridge configuration. inputs are probably coming from the PCI bus.
How on a PC we (or them) select which ports are read from each bus ? This one has no such options on the bios config.
lc.
cs snipped-for-privacy@hotmail.com wrote:
Try to get the data sheet for the bridge chip, or more likely the motherboard chipset
More directly, do you have a known-good pc104 card you can try?
Will search the data on the isa bridge chip, maybe we can configure it after the boot at the beginning of our code... or maybe not :-(
no other PC104, but many trivial PC's w/ isa and they do work beautifully. ;-) Opss I think we have an older P1@100MHz in PC104 format, will look.
tks.
lc
cs snipped-for-privacy@hotmail.com wrote:
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