Re: Original Apple IIc serial inaccuracy (?)

[David Wilson <mcs6502@gmail.com>]

On Jan 2, 10:27 am, Mitchell Spector <mitch...@hotmail.com> wrote:
>     I don't think it affected serial printers as much as it did modems
> (if at all), as they were less particular about timing. I remember some
> documentation of the issue claiming it only affected port 2 (modem)
> but then the same 6551 ASIC did control both ports 1 and 2. At best
> guess they were simply referring to modems as that is what normally
> would connect to port 2.

I think you mean the 6551 ACIA (Asynchronous Communications Interface
Adapter (aka UART or Universal Asynchronous Receiver/Transmitter to
our PC friends)).

ASIC = Application-Specific Integrated Circuit

Both the port 1 and port 2 6551 ICs share a common clock source
(although interestingly on the circuit diagrams in the 2nd printing of
the IIc Technical Reference Manual, there is an option shown in dotted
lines to add a 1.8432 MHz xtal to the port 2 6551 leaving the other
6551 with the slow clock).