I've bought another RS232-current loop adaptor to try to connect my ASR33 Teletype to my Altair clone after the old adaptor stopped working. This one has 5 terminals marked TB1 thru TB5 and for active-transmit and active-receive the connections seem to be:
TB1 TX I+ Out / V+
TB2 nothing
TB3 RX I+ Out / V+
TB4 nothing
TB5 TX/RX I- In / V-
My problem is figuring out which of the four wires from the ASR33 to connect to which of those 5 terminals. On my old RS232-current loop adaptor, the following connections worked:
TTY red wire to adaptor terminal K that is labelled R-
TTY white wire to adaptor terminal G that is labelled T-
TTY blue wire to adaptor terminal J that is labelled GND
TTY black wire to adaptor terminal M that is labelled GND
The mytery is that, using this old mapping that worked, the Teletype seems not to have wires for T+ or T+ at all: the current seems to flow between T- and GND and between R- and GND. Can anyone figure out how my four Teletype wires map onto the five terminals on the new adaptor? Also, I presume I should set the new adaptor to 20ma, Active Transmit, Active Receive, and DCE (not DTE), right? I supply current to the adaptor using a USB cable that came with it. On the Altair side of the adaptor the connection is a DB-25 serial port female socket and since the Altair serial ports are also female I use a 25-pin male-to-male gender-changer to plug the adaptor into the Altair. Any of that sound wrong?
The instructions for the new adaptor are here:
http://gabrielegan.com/scratch/new-RS232-current-loop-adaptor.tifAnyone's thoughts on what I'm doing wrong would be much appreciated.
Regards
Gabriel Egan