lacasse%rand-unix@sri-unix.UUCP (05/27/83)
RE: So I connected both the terminal and the serial line to the interface at
once and -- When I typed at the keyboard, the printer would print that
character. Does anyone out there know what might explain this?
When you did this, it sounds like you had Transmit-Data from the terminal
connected to Receive-Data on the printer. Try reversing pins 2 and 3 on the
printer. If you connect the Receive-Data lines of both printer and terminal
to the DLV-11J Transmit-Data (and all grounds, pin 7), and then send
something out from the CPU, it would be interesting to see if it shows up
of the terminal, but not on the printer.
General RS-232 notes: Up to about 4 receiving lines can be connected to
one transmitting line (with standard MC1488/MC1489). Another nice thing
to know is that the standard drivers are short/cross connect burn-out
proof. (But beware of hobby stuff with +5 on pin 25 and such!) If your
documentation is not clear and you can't look inside, you can tell a
transmitting line from a receiving line by loading the line to ground with
a 1Kohm resistor, and measuring its voltage. A receiver will show about
0V. A transmitter will show a rest state of about -12 volts for one of the
data lines; and -12 (NO) or +12 (YES) for one of the status line.
mark lacasse (lacasse@rand-unix, 213/393-0411)