RE: 6522 vs 6526 (was Re: 6502 to 8501: new details)
Date: 2002-02-28 09:58:30

Hallo Spiro,

> I also seem to remember that connecting a 6821 to the 6510 
> might (i.e., it depends upon the particular "instance" of
> the device used) require the same work as connecting a 6522

You can connect a 6821 directly to the bus of a C64, but you can NOT with a
6522. This has to do with the fact that the addressbus must be stable when
CLK2 goes (H). One trick to connect a 6522 to a C64 is delaying the rising
edge of CLK2 by using a 7474 D-flipflop.

CLK2      -> D-input, CLeaR-input
DotClock  -> CLocK-input
+5V       -> PReset-input
Q-output  -> CLK2-input 6522

While CLK2 is (L) the Q-output remains (L) as well. When going (H) it
enables the 74 to react on pulses coming from the Dotclock. The first
positive flank is 62.5 ns after the rising edge of CLK2. 

> but the 6510, 6526 and 6567-6569 do not belong
> there, literally, because of timing differences.

IIRC the original C= IEEE-interface uses a 6525, isn't it? If so, you can
share the 6525 amongst the above IC.
   / __|__
  / /  |_/     Groetjes, Ruud
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