Re: TOD on CIA

From: Nicolas Welte (
Date: 2000-10-25 09:44:25

William Levak wrote:
> It has two 6522's and a 6526.
>       VIA1  $1800-180F  serial bus
>       VIA2  $1C00-1C0F  drive mechanism
>       CIA1  $4000-400F  fast serial bus
> The only thing used in the 6526 is the parallel port B, SP, and CNT.
> Since the system uses this port for fast communication, it may reset your
> information during normal operation.  You may have to load a routine to
> the drive memory that disables the system interrupts in order to use the
> TOD.

I think the TOD input of the 1571 CIA is just not connected to anything.
Also note that some 1571 were even shipped with a 8520 CIA (from Amiga),
which has the TOD clock replaced by a straight binary counter.

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