Date   : Mon, 28 Jan 1985 11:20:00 PST
From   : R. MEIER <rmeier@Su-Star.ARPA>
Subject: re:apple-cpm serial interface problems

Jim,
       I have the following arrangement of cards and have not had a problem.
               Slot 0:128K ram
               Slot 1:Super-Serial Card (modem)
               Slot 2:Apple Serial Card (printer)
               Slot 3:80-col card
               Slot 4:Z80 card
               Slot 5:vacant
               Slot 6:disk
               Slot 7:vacant
       Within the configuration block of CP/M, I have routines to make the
128K ram look like a disk, the Slot 2 Apple Serial Card look like a printer
with DTR flow control, and the Super-Serial Card look like another console.
The Apple Serial Card has no flow control on board, but since the printer
doesn't transmit, I switched the DTR and REC lines on the RS-232 connector.
The Apple Serial Card is nothing but a ROM, line driver, and line sensor
that I can read/write directly.  The ROM contains software for RS-232 timing,
so I use it to output a byte at a time, but I only send it a byte after
reading that the DTR line is high.  The Super-Serial Card has flow control
on board and so is called in the normal fashion of a port/status register
pair.
       If the above superficial view is helpful, then fine, otherwise,
write me at rmeier@star.arpa.
                                       Bob (rmeier@star.arpa)