Hi Donald,

Three comments:

1.  Have you looked at the "Parallel Slave Port" on the 40 Pin PICmicro
MCUs?  I have wired PICmicros to the ISA bus using this feature with just an
address decoder.

2.  For your application, you will have an issue because in this mode, you
will only be able to read/write to one address (not 256).  To access
multiple data bytes, you will have to come up with some kind of address/data
protocol.  This is a good thing because:

3.  The I/O space of the PC is very limited (for ISA, you should restrict
yourself to the address range 0x0100 to 0x03FF) - yes, the full I/O Space
address range is 64K, but only the first 1024 addresses are available for
peripherals and there isn't 256 contiguous addresses that can be used.
Using addresses above 0x0400 may result in conflicts with other devices
which should only be accessed by BIOS.

myke

----- Original Message -----
From: "Donald L Burdette" <dlburdette@JUNO.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Sunday, January 14, 2001 10:56 PM
Subject: [PIC]: ISA peripheral


> Hi all.
>
> I want to put a PIC as a peripheral on the ISA bus, which is controlled
> by a PC104 embedded computer running some version of DOS (don't know
> whose, but probably not MS).  The PIC would be an IO device, mapped as
> 256 bytes of IO space.  The problem is that the PIC isn't fast enough to
> watch the address select line (decoded externally), read the 8-bit
> address, look up a data value, and put it on the data bus before the ISA
> needs it.
>
> I've thought about using a simple flip-flop to activate the /IOWAIT line,
> but there's a limit as to how long you're allowed to hold that line.
> It's two microseconds, and I don't think that's long enough.  Is there
> any problem holding this line longer?  I think I would need less than 10
> uS, maybe more like 4 or 5.
>
> Has anyone had any experience in this area?  Any advice?  Good place to
> look for working circuits?
>
> Thanks in advance.
>
> Don
>
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>
>
>

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