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 disassembler? Richard - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail cbm-hackers-request@dot.tcm.hut.fi.
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