knudsen@ihnss.UUCP (12/16/83)
Jones has a good idea. The connector between the Coco PC board and the keyboard is a good source of two 8-bit parallel ports, one in, one out (or you can program the PIA differently for any mix of In or Out bits). You can just solder wires right across the connector pins in parallel with the existing connections, provided you don't touch the original keyboard while your special application is running. Some other considerations: (1) If your machine powers up with the conventional keyboard drivers first, your added hardware must "lay low" until you boot in your new drivers. (2) Some missing key(s) are used for the memory-size jumper, to tell BASIC how much RAM you have. Your hacks must not mess this up. Converesely, the RAMsize jumper may mess your stuff up. Be prepared. (3) Good news--the input PIA port on the existing keyboard is just open- collector, so you can hook your "real" keyboard directly in parallel, no multiplexer needed. (4) Keyboards with parallel ASCII output consist of more than just keys and wiring; they need lots of logic, or a dumb micro (8748, etc) to translate into ASCII, especialy when SHIFT and CTRL keys get into the act. (5) I've considered mounting a DB25 (RS-232 style) connector on the bottom side of the Coco case and wiring it to the keyboard pins as mentioned above. Just using the built-in POLCAT, such connecyor can be used for numeric pads, contact-closure detection (robots, anyone?), etc. etc. Maybe stick a decent 8-bit D/A converter on the output..... enjoy, mike k