Troubleshooting RS232/RS422 Serial Interfaces

Here are the most common sources of interfacing problems and tests you can make:

Loopback Test

  You can verify that the Antona adapter is working by doing a simple loop-back test using a male DB9 connector with pin 3 to 7 and pin 8 to 2. Use a simple terminal program to just test that characters sent out the com port are echoed back through the adapter. Make sure that your terminal program is turning on RTS and DTR to power the Antona adapter, and that the program is set to control the com port that the adapter is connected to. The adapter operation does not rely on baud rate, parity, stop bits - but the actual application program you are using with the adapter may (see PROGRAM OPERATION).

CABLING (most common problem)

  If one of the wires used is not connected or shorted, the whole interface will appear not to be working. Try using another cable or try the loopback test described above with the cable to verify operation. If you can not get the loopback test to work through the cable, it for sure will not work in your application.

  Take a look at the manual of the RS422 equipment that you are trying to control. Be sure that the pin definitions on the RS422 equipment tells you the signal names, not what they are suppose to connect to. This sounds simple, but unless you know which direction the pinouts are defined from, you will connect TX+ to TX+ which is incorrect. Make sure that you have the TX+ on the Antona adapter connected to the RC+ on the RS422 equipment and TX- connected to RC- (same for the signal coming back from the RS422 side - make sure that the Antona adapter's RC+ is connected to the TX+ and that the RC- is connected to the TX- on the RS422 side. Pin 5 on the Antona adapter's RS422 output side should be connected to the ground of the RS422 equipment.

  When shipped the Antona adapter is set for a SMPTE MASTER interface (connector pinouts are in the 6000 series manual for both MASTER and SLAVE mode, so be sure you are looking at the correct table). You may also want to open the Antona adapter up and verify the jumpers are set for the mode you desire. All 4 jumpers should be installed, they each represent one of the 4 signals being transmitted and received.


  Be sure that the RTS and DTR line on your RS232 interface are high - this is what powers the Antona adapter (like a mouse interface). Some portable computers just don't have enough power to run the adapter and/or the RS422 piece of equipment you are interfacing to may be over a long cable run and/or terminated with a 150 ohm resister (you can try disconnecting the termination resister also - some types of equipment give you a jumper option for the termination resister), so it might be necessary to externally power the adapter through the RS422 side by applying +5v to +12v DC power to pin 9 and ground to pin 5 or 1.

Program Operation

  The application program you are using may need some setup performed - selecting the com port, baud rate, parity, number of data bits, stop bits and setting the level of the handshaking signals (RTS and DTR lines high to power the adapter). Usually, for multimedia type interfaces, the baud rate is 38.4 Kbaud, Odd parity, 8 data bits and 1 stop bit. Here again, if the program is not setup right, the adapter will appear not to be working at all.

RS422 Equipment

  Try to verify the operation of the target RS422 equipment independent of the Antona adapter by using another setup - a different cable connected to another RS422 signal generating device would be the best. Using a different computer with the Antona adapter would also be a good test.

Now What?

  If none of the above seems to fix the problem, but the loopback test works, the adapter is working and you may now need to connect an oscilloscope up to examine and monitor the RS422 signals and the RS232 signals being generated by the Antona adapter with the plastic cover removed and running with your RS422 device and program. Refer to the schematic at in the ANC-6000 User's Manual you received with the adapter. It's easy to put a scope probe onto the tops of the 4 jumpers and verify that RS422 signals are coming and going to the adapter. Test the +power to the adapter by attaching a probe to the +lead of the 4.7uf capacitor near the +5v regulator (LM2936). Look for excess noise on any of the lines that might be fouling up the transmissions.

  If the loopback test does not work, connect a temporary external power supply up to the adapter by using a +9v battery and battery clip wired onto the loopback connector described above. Each adapter is tested prior to shipment with every combination of characters transmitted and received at 38.4 Kbaud, but like everything, occasionally they can go bad. Of the hundreds we have shipped, there have been maybe 10 or so that arrived non-operational. Damaged in shipping or infant component burnout. We do warranty our adapters, so if it still does not work, call Antona and we will work out an adapter exchange.

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Updated 02/21/09 12:00

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