Re: PCcard (2)
Date: 2001-04-09 14:47:30

On Mon, 9 Apr 2001, Ruud Baltissen wrote:

> Hallo allemaal,
> Had some big interest for my IDE- and PCcard-project last weekend. That's
> why I need my lost document. Some German chaps were (more then) playing with
> the idea of attaching a PC-network card to a C=. Building the PCcard enables
> one to attach this networkcard AND an IDE-interface and others...
> So I'll design a new card. In some earlier mails I mentioned to use a 6522
> but I thought that if I wanted to include DMA later, I needed some means to
> tristate the addressbus. And that difficult when using a 6522. But found
> another trick to reduce the solder work a little bit.

If you're wanting to do DMA from an ISA card, you can have the DRQ lines
cause an interrupt on the c64, which would react by tristating the 6522(s)
and then asserting DACK.  After this, you can use "Pseudo DMA", which
consists of convincing the card that its on a (very slow) DMA channel by
manually toggling the lines to clock data in.  Mind you, ISA's dma doesnt
provide the destination address from the expansion card.  It's actually the
DMAC's responsibility to do this, so we dont need to change the address
lines.  We simply provide ISA bus signals. *wink*

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