RE: JIffyDOS Coding

From: Richard Atkinson (
Date: 2001-03-28 18:33:00

On Wed, 28 Mar 2001 wrote:

> >On the plus/4, DATA is output from bit 0 of the 8501 I/O port (inverted)  
> >and CLK from bit 1. However, DATA is read in from bit 7 whereas CLK is on
> >bit 6 - ie. the order of the signals is reversed.

> Thanks for the info. To complete the picture, where is ATN connected to?

ATN out is bit 2 of the on-chip I/O port. Like the 64, it is only
available as an (inverted) output.

The nice thing about the 264 series is that because the serial bus uses
the processor I/O port, reads and writes of the port can use zero page
instructions. Hopefully this will compensate in part for the slower clock


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