RE: Article PC-card
Date: 2001-02-27 12:09:02

Hallo Nick,
> A 1.44Mb floppy interface using DMA has been done by a guy in Hungry...

Thanks for the info. I'll have a look.

> How do you know that read/writes to the RAM won't clash with the VGA
> controllers accesses?

For accessing the memory or I/O different lines are used: MEMW/MEMR and 
IOWR/IORD. You only activate that line which is needed for the specified 
operation and area. A C= does not have these lines. So you have to generate 
all four of them. One thing you should know too that these lines are used 
for timing as the 65xx ICs use CLK2. A C= does not have a sepperate I/O and 
memory area. So I used an I/O bit to make a difference between a memory- or 
an I/O-operation.

So I combined the R/W, CLK and an I/O bit using a 74LS138 
(3-to-8-multiplexer) to generate the four needed signals.

Groetjes, Ruud

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