Re: Article PC-card

From: Nicolas Welte (
Date: 2001-04-04 11:27:50

Spiro Trikaliotis wrote:
> I remember seeing an article giving a solution to this problem by delaying
> one edge (according to your description, it must be the rising one) of PHI2.
> Anyway, I don't know where that was. Anyway, I remember that the author also
> mentioned that in most cases, this delaying is not necessary in reality, so
> the 6522 (or 6821, with the same problem) should work good in the C64, too.

I remember that one approach was to delay Phi2 with an LS74 flipflop by one
dotclock cycle, but I'm pretty sure that the 6821 does not need this delay. I
have a few 6821 expansion port circuits (like IEEE488 interfaces, or the
Formel 64 module, the Prologic DOS expansion port interface, the Quickbyte II
Eprommer) and none of them uses a clock delay.

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