RS-232 Serial Port Troubleshooting

Haas machines using a serial port connection (generally manufactured prior to 2016) will need to incorporate a Moxa box (serial-to-ethernet converter) in order to send data to Machine Metrics due to the absence of an Ethernet port on the machine's control.  RS-232 serial ports use fairly old technology, and this can create difficulty when troubleshooting a machine that has stopped reporting. 

This article will talk about how to use a testing device to determine if there is a communication problem between the Moxa and the serial cable.

Additional Resources

For more information about the Moxa box, visit our Knowledge Base article here.

For more information about Haas Serial, visit our Knowledge Base article here.

For more information about Haas Next Gen, visit our Knowledge Base article here.

An RS-232 tester (pictured below) can be purchased from many sources online and is useful to determine if there is continuity between the Moxa and the serial cable.  There are LED lights on the tester that can indicate where a problem lies if there is one.

In the above picture, the tester is attached to one end of a serial cable, while the other end is connected to the Haas serial port:

Please Note:  This is through a null-modem cable (crossover cable), so at the other end of the cable the Haas serial port is holding TXD negative, which gets crossed-over to RXD on this end.

RXD (Received Data) is the data input signal at the Moxa.
CTS (Clear To Send) is a control input at the Moxa. ON it means “Haas is ready to accept data from the Moxa”

On the RS-232 tester, green = negative which is 1 for TX/RX, but OFF for CTS/RTS, and red = positive, 0 for TX/RX, ON for CTS/RTS.

In the above picture, the tester is connected to the Moxa:

TXD is held negative (=1)
DTR is held negative (OFF)
RTS is held negative (OFF)

Please Note: The Moxa’s Link and Tx/Rx lights are off, indicating there’s no ethernet connection and no RS-232 data activity.  

Have Questions?

If you have additional questions about Haas Serial connections or how to test cable continuity, please reach out to our support team at support@machinemetrics.com.