Re: VIC-1011A

From: Marko Mäkelä (
Date: 2001-05-29 10:00:52

On Tue, 29 May 2001, Carlsson, Anders wrote:

> Also, there might be ROM bugs on the VIC-20 when dealing with RS-232
> communication. I have an early issue of a Swedish VIC magazine where
> an user had disassembled parts of the ROM and found what he considered
> to be actual bugs and some non-bug oddities.

I would have understood that on the C64, since the first KERNAL ROM
version (901227-01) assumes a system clock of exactly 1 MHz, which is true
on the UltiMax but maybe not on any C64 board.  (Do early NTSC boards have
a separate 8 MHz crystal for the dot clock in addition to the 14.318181
MHz color clock?)  The second KERNAL revision (901227-02) contains code
for detecting PAL and NTSC, and has two separate RS-232 timer tables for

On the VIC-20, there are separate KERNAL ROMs for PAL and NTSC.  The only
versions I'm aware of (ignoring localized versions) are 901486-06 (NTSC)  
and 901486-07 (PAL).  The BASIC ROM is strangely 901486-01 (it has the
same "base number").  Did Commodore start the KERNAL ROM numbering from
-06, or were there perhaps older KERNAL ROMs?

> If anyone wants to know more about this subject, I can bring the paper
> some other day and translate the letter.

I don't expect the magazine to list the firmware versions (since people
probably didn't dare to open their expensive computers back then), but I'd
like to read the article.  If possible, please post also the original.

> /Anders Carlsson, has never used RS-232 on his VIC-20

Me neither; I've only tried it on the C64 and was severely disappointed.
But I must say that using a 80-column PET as a terminal would be cool.


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