knudsen@ihnss.UUCP (09/30/83)
Of the many wish-list features we'd like to add to Cocos, some are easy for hardware hackerss to build themselvess (and sell). Others are not. SSome easy add-ons: real UART, higher-ressolution A-D & D-A converterss, parallel ports, speech synthers, home & industrial controls, etc. These can all be plugged into the cartridge bus. Radio Shack sells two sizes of PC board with the perfect 40-pin fingers already built in for $5 and $10. Harder to add: Real (80x24) CRT terminal driver (6845 is the chip, I think). This has to DMA (cycle-steal) from the CPU and the SAM, which can be tricky. (Actually, Motorola could have easily provided a SAM mode to refresh an 80x24 character generator chip; the badwidth is there). Damn near impossible (if not, pleasepost!): Add memory management/expansion. Motorola makes a powerful MMU chip for the '09, and a otorla sales engineer personally assured me that it can work with a SAM (6883). It always adds one exxtra cycle to every RAM access in our already slow processor. However, this MMU must be inserted between the CPU and the rest of the machine, which is a lot of cutting in a Coco. Better to start from scratch. Not hard: Winchester controller. Plug in the bus like the floppy. To take advantage of higher data rates, you may want DMA. To do this right, you must bring out a couple of 6809 status pins that are N/C in the Coco. I plan to mount a small connector on the back near the cart slot for such purposes. Keep 'em hacking, mike k