BTX decoder ROMs

From: Richard Atkinson (
Date: 2000-07-06 16:16:54

As some of you may have seen from comp.sys.cbm, I have dumped the ROMs
from two versions of the Commodore BTX decoder. My father also bought me a
digital camera as a graduation present (hooray!) so I will be taking
pictures of the insides and outsides of both versions. The second, more
common decoder looks like the most interesting. Basically it is a 6803
second processor for the C64 with 64K of RAM, an onboard UART for a
limited version of RS232 (1 start bit, 1 stop bit and 8 data bits I think)
and a 4096 colour RGB display.

The 6803 also has a hardware multiply instruction which executes in 10
cycles (two eight bit accumulators multiplied together and stored in low
high format in the same accumulators) so I think it almost qualifies as a
C64 math coprocessor.

ROMs for these two decoders should be on funet shortly, and the 2nd ROM
(32K long) is most interesting. It looks like the 6803 initialises first
and copies parts of the BTX ROM into C64 RAM to look like an autostarting
cartridge. What happens then I am not certain; does anyone have an 6803


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