knudsen@ihnss.UUCP (10/03/83)
I checked my Technic Ref Manual for Coco and was amazed to find that the CTS- (Cartridge Select) line is horrendously low-pass-filtered! Not just a 470 ohm resistor in series, but a 220 pf cap shunt to ground after that. I think the numberss were R80 and C7x. The Cap is right by the connector; R80 is in the center of the board. These parts caused the CTS- enable to look more like a sine wave than a digital pulse! After persuading these components to depart from my Coco's innards, I now have a digital signal. I guess home computers are like cars-- you gotta remove a few air-pollution government-pacifier parts to get full performance. (I noticed NO more interference on my TV set afterwards.) Can now run speed POKE &HFFD7,0 with disk in, but you can't really USE the disk due to software timing loops (head seek goes ape). Trick is to add code to slow down machine during I/O, run fast rest of the time. Also note that the ROM chips in utility cartridges like BASIC-AID and SDS-80C are themselves too slow to run in fast mode.