Re: Strange (whoops!) //c problems

[dempson@actrix.gen.nz (David Empson)]

In article <4uu0cs$mcf@balsam.unca.edu>, RKFAIRCLOTH@unca.edu (Rhonda K.
Faircloth) wrote:

>Whoops! I've made some mistakes. I'm going to have to run the self test in my
>brain to be sure it's working. :)
>
>My //c is the oldest version, PEEK(64447) returns 255, not 0.

I thought that might be the case.  The original IIc ROM (255) does not
have a proper self test.  It just runs through a loop showing graphics
screens and doesn't produce any useful results.

The self test was implemented in the UniDisk 3.5 version of the ROM (peek
returns 0) - they doubled the size of the ROM, so there was plenty of
space todd missing features.

>On another note, I seem to recall that the oldest //c's also had
>some timing problems on the serial ports. Was there something other
>than a one-chip-ROM-upgrade that needed to be done in order to fix
>this?

It requires a motherboard modification, replacing a chip with a crystal
oscillator.  Apple never did this as a modification - they simply replaced
the motherboard when the user could demonstrate that they had the problem.

The problem is that the original IIc motherboard uses a cheap method of
generating the baud rate clock for the serial chips, which results in baud
rates that are about 3% slower than the standard.  This is enough to throw
out some intelligent modems.

The revised motherboard used a crystal oscillator with the correct frequency.

-- 
David Empson
dempson@actrix.gen.nz
Snail Mail: P.O. Box 27-103, Wellington, New Zealand