18 Sep
2013
18 Sep
'13
1:29 a.m.
From: Josh Dersch <derschjo at gmail.com>
Date: Tue, 17 Sep 2013 21:09:46 -0700
Subject: Re: PDP-8/L current loop -> RS232 help
Sorry to reply to my own post here, I had a bit more time to screw with
this this
evening. Turns out it was a programming error (actually a
program entry error :)) that was (apparently) causing the 40mA current
instead of 20mA -- the >little "echo" program I coded up wasn't properly
waiting for data to come in before echoing it back, so the 8/L was
constantly sending 377 back across the loop, which I'm assuming accounts
for the difference?
With this corrected, the loop is registering ~23mA
idle, dropping to
19-20mA when the PC attempts to send data. Can anyone comment on
whether
this sounds reasonable? Anyone have any advice? (Getting desperate here
:)).
Thanks,
Josh
If you intend to use your serial interface with to load RIM/BIN formatted
tapes you may need to implement the READER ENABLE signal. This signal comes
from the M706 module and goes to the CTS signal on the
serial port. Your
terminal emulator can be programmed to only transmit when the CTS
signal is
active. This signal will also allow you to modify the TTY port to run at
much higher speeds than the standard 110 baud.
--
Michael Thompson