Multi USB/RS232/RS485/TTL Converter (TEL0070)

This is a placeholder topic for “Multi USB/RS232/RS485/TTL Converter” comments.

Multiplexer has a set of interfaces for a variety of multi-function adapter plates. It supports USB, TTL, RS232, RS485 interfaces between the system conversions. What’s more powerful is that it also supports one input multiple outputs, which greatly facilitates the communication between various controllers.

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Hi guys, I have a digital read out (dro) on a small lathe. All DB9 plugs , female on the dro unit. Paperwork says RS485 for the unit. Pin one is 5V pin 2 is 0V, pin 3 is A and pin 4 is B. Pins 5 to 9 are blank. Seems to work correctly with supplied glass linea readouts. However I wish to fit a smaller read out on one axis. The new glass read out has a DB9 plug and specifies RS232 on the paperwork and has TTL printed on the sensor / glass readout. Doesn’t work plugged directly together. Doesn’t work with a cheap converter rs232 to rs485 (port powered ) . Would your part number 0070 work ? I can supply pictures of the plug wiring .

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Hi Andrew
RS485 is a balanced line system. Pins 1 & 2 are self explanatory while the A and B are each side of a balanced line. Similar to balanced audio with the same advantages, Resistance to outside interference and the ability to be used over very long distances. The down side is it is only one way at a time coms, ie; dedicated one way or half duplex. A full duplex system requires 2 circuits.Having said that the advantages over some distance vastly outweigh the disadvantages.

RS232 on the other hand is an unbalanced 3 wire system, Gnd TX and RX, the TX and RX are usually crossed over in the cable for obvious reasons. “Normal” installations are only recommended for a couple of metres but using 2 pair techniques and very low capacitance cable distances of something like 70 metres can be achieved.

Because of its short distance capability any converter should be fitted at the RS232 end, in your case the additional display.I am not familiar with the available converters but the terms TX and RX should be investigated and clarified. Do the terms refer to TX and RX out and in to the converter or do they refer to TX and RX of the host unit (your display). Examination of the circuit would be required to establish this. This is maybe why yours did not work. Was TX and RX reversed???
Beware of some converters. They seem to have pull up and pull down resistors on the A and B RS485 lines. I don’t know why and what they would do is unbalance the line so losing all the advantages of the balanced system. I would stay clear of these or remove them if possible. The same applies to any terminating resistor. This should only be at the END of a cable run.

While I am here we may as well get something else right. The Sub D connectors you refer to should be DE9, DB signifies a 25pin shell size. DE 9 pin, DA 15pin, DB 25pin, DC 37pin and DD 50 pin. These signify shell sizes and have High Density pin variants. Like DE15 or so called VGA video connector on computer/monitor cables which is a 15 pin connector in a 9 pin size shell.
Cheers Bob

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