🚀 go-pugleaf

Vincent Wass (vwass@sdcc13.ucsd.edu) wrote:
: I am having trouble with a computer interface project.  I'm trying
: to decode addresses on the bus for my own plug-in wire-wrap card.
: 
: My only problem seems to be that while the card is plugged
: in, both of my disk drives (5 1/4, and 3 1/2) have some sort of
: problem copying files to my hard drive.  When I type chkdsk at the
: 
: 
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The Pc Bus has a signal called <something like> CPUAEN that tells you if
it is a CPU cycle or a DMA cycle. All IO devices must include this signal 
in their decoding and not respond unless it is a CPU cycle.

Whats happening is that the system is doing a disk read into memory that
has the same address as your IO card. Your card sees the proper address 
and the IORead strobe intended for the disk controller and promptly
blows away the data on the data buss.

John Eaton
!hp-vcd!johne