Hi, I had a question about using the PC/104 bus on the TS-7250.
I have a device (16 bit) I wish to connect that supports both byte and word
accesses, as
such, it needs both a BHE (data high enable) and BLE (data low enable) signal
-- both
active low.
Since only the BHE line was pulled onto the bus, I was wondering what happens
to the A0
(Address Line 0) line during word accesses?
If during a 16 bit access it's still valid, hooking A0 to the BLE on my device
should allow it
to do what I need:
Even address byte accesses (BLE(A0)-LOW BHE-HIGH)
Odd address byte accesses (BLE(A0)-HIGH BHE-LOW) -- (by treating
a odd byte access
as a word access, but shifting the byte to the higher data lines)
Even address word accesses (BLE(A0)-LOW BHE-LOW)
Odd address word accesses (BLE(A0)-HIGH BHE-LOW) -- It is okay
that this case will
fail.
i.e., am I correct in saying
if I do outb(value, 0x89000000), will A0 be zero? -- Byte at even address
if I do outw(value, 0x8b000000), will A0 be zero? -- Word at even address
if I do outw(value, 0x8b000001), will A0 be one? -- will it allow me?
This would be
used for a byte at a odd address.
(where 8 bit IO is mapped to 0x89000000 and 16 bit IO is mapped to 0x8b000000.
The
device base address is 0x0).
In any 16 bit implementations I've seen, A0 is usually left disconnected and A1
becomes
the LSB (so accesses can only be done on word boundaries).
Does anyone have any experience with this?
Thank you.
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