Google Groups no longer supports new Usenet posts or subscriptions. Historical content remains viewable.
Dismiss

ISA bus logic: Memory mapping question

0 views
Skip to first unread message

Russell Magee

unread,
Sep 12, 1997, 3:00:00 AM9/12/97
to

Hi all,

I'm designing some simple ISA bus (PC/104 actually, but it's the same
except for the actual shape of the card), and I have a question regarding how
ISA cards impose their memory on the PC's local memory map.

What we need to do is make some dual-port RAM on the card visible on the PC's
local bus within a certain (programmable) memory block. I have I/O register
access working fine already.

For instance, a VGA card makes its RAM visible in a certain 'window' which
overrides the local DRAM which would otherwise be present at that location. How
exactly is this done? I have the IEEE P996 specs (the 'official' ISA bus
document) and it seems to imply that the MEMCS16* line must assert within a
maximum time from the LA (latched address) lines becoming stable. Is this the
right interpretation?

Thanks a lot in advance,
Russ Magee,
Steady State Automation Ltd.


0 new messages