I need to interface with a motor controller through RS232. I am using an arduino for this. The datasheet has a page on RS232 interfacing shown below, could someone please identify what I would need to communicate with this from an arduino?

serial datasheet page

there are no details on the RS232 voltages, as far as I know following the standard I should be able to communicate with lines from 0 to +3.3v since this lies within the spec of 0v to +3 - +12v however so far I am unable to get a response from the device by connecting Tx, Rx, and GND to a ttl logic USB serial device, nor my arduino.

Using the RS232 cable supplied with the controller I am able to communicate both with the supplied software and through a serial COM port sniffer, so I am sure my data addressing is correct.

I feel like there is a perhaps a voltage level difference issue, or maybe i need to control the other pins however I was under the impression these were optional, could someone please shed some light?


  • 1
    \$\begingroup\$ RS-232 requires an inverting level shifter, connection without that will damage your Arduino. Ironically the oldest Arduinos had that an a 9-pin connector, with the USB being a subsequent replacement. \$\endgroup\$ – Chris Stratton May 28 '17 at 20:48
  • \$\begingroup\$ check your DC static levels for idle to confirm active and correct polarity and note jumper between pins 5,7 \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 May 28 '17 at 21:08

A TTL to RS232 shield is one solution

https://www.sparkfun.com/products/13029. Details in DOC links will give more clues.


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