M200 interfacing

Sellam Ismail <foo(a)siconic.com> wrote: Except that, if you want to read binary cards (trust me, you will -- those binary cards are contain boot and other code for these machines), you need to do all 12 rows. 80 columns x 12 rows = 960 bits / 8 bits per byte = 120 bytes per record. OK, now as for sending that over a serial line, remember that serial I/O adds framing information , so it becomes 10 bits per byte supposing 8 data bits, no parity, 1 start and 1 stop bit. So 1200 bits at 9600 bps = 0.125 second. You probably want to do at least a simple checksum of the data for each record and send that too (so the receiver can verify, send ack or nak, and the sender can retransmit on receipt of nak or just non-receipt of ack). You've got RAM in the Apple, use it as a buffer between the card reader and the serial port. 16KB would hold 136 full card images, which you might think would be more than enough time to tell the reader to stop picking cards and actually have it stop. So, when the buffer's fullness gets above some threshold, stop picking cards until it gets below some lower threshold. You may be able to do some cheap buffer- and serial-time savings by either run-length encoding or just keeping a record length and not storing or sending trailing blank (unpunched) columns. Depends on your data. I think I would go for this last. -Frank McConnell