RS-232 to current loop (again)

General discussions related to the Altair 8800 Clone

Re: RS-232 to current loop (again)

Postby AltairClone » August 9th, 2017, 4:49 pm

I've always wanted to make an RS-232 adapter for the Teletype that simply plugged into P2 (one of the eight molex connectors on the back of the UCC). No other wiring is required. Power is available on the connector (48 vac) and the current loop signals are present on P2 as well as on the terminal strip.

Mike
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Re: RS-232 to current loop (again)

Postby toml_12953 » August 10th, 2017, 2:53 am

AltairClone wrote:I've always wanted to make an RS-232 adapter for the Teletype that simply plugged into P2 (one of the eight molex connectors on the back of the UCC). No other wiring is required. Power is available on the connector (48 vac) and the current loop signals are present on P2 as well as on the terminal strip.

Mike


So go ahead and make one! If you plan on actually doing it, please add me to your list of buyers and notify us when it's ready to ship. Thanks!
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Re: RS-232 to current loop (again)

Postby AltairClone » September 3rd, 2017, 10:16 am

Has anyone ever seen an ASR33 with a UCC-6 with anything plugged into P1 or P2?

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Re: RS-232 to current loop (again)

Postby toml_12953 » September 3rd, 2017, 3:19 pm

AltairClone wrote:I've always wanted to make an RS-232 adapter for the Teletype that simply plugged into P2 (one of the eight molex connectors on the back of the UCC). No other wiring is required. Power is available on the connector (48 vac) and the current loop signals are present on P2 as well as on the terminal strip.

Mike


So what's stopping you? :) I'd buy one to get rid of the tricky B&B interface I have now. It works but hangs down the back and can be a pain to keep connections.
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Re: RS-232 to current loop (again)

Postby mail@gabrielegan.com » September 9th, 2017, 3:57 am

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.tif

Anyone's thoughts on what I'm doing wrong would be much appreciated.

Regards

Gabriel Egan
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Re: RS-232 to current loop (again)

Postby AltairClone » September 9th, 2017, 1:08 pm

I'd set the switches to 20, DTE, ACT, ACT

Adapter pin 1 to Teletype terminal strip pin 7 (data to Teletype+)
Adapter pin 5 to Teletype terminal strip pin 6 (data to Teletype-)

Adapter pin 3 to Teletype terminal strip pin 4 (data from Teletype)
Adapter pin 5 to Teletype terminal strip pin 3 (data from Teletype)

Mike
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