Antona Troubleshooting SMPTE Serial Interface to RS422 Equipment

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 interface wires used is not connected (open) or shorted, the whole interface will appear not to be working. Try using another cable or try the loopback test described above at the end of 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 RS485/422 equipment that you are trying to control. Be sure that the pin definitions on the 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 RS485/422 equipment and TX- connected to RC- (same for the signal coming back from the RS485/422 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 RS485/422 side. Pin 5 on the Antona adapter's RS422 output side should be connected to the ground of the RS485/422 equipment.

When shipped the Antona adapter is set for a SMPTE MASTER interface. Connector pinouts are in this manual for both MASTER and SERVER (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 JP5/6 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.

2-Wire RS-485 Multidrop Cabling

Check to make sure you have connected the plus signal lines to the like ‘plus’ signal lines and ditto for the negative to the negative signals. Try connecting just one piece of equipment to the adapter for debugging both the cabling and the software interfacing. Remember that multidropped peripherals must each be assigned a unique device code. Check with the specific equipment's User Manual for setting this, along with baudrate, character length, parity and stop bits.

Cable Termination

Reflected signal produced by cabling that is not terminated properly will cause data transmission errors. A terminated cable matched to the impedance of the cable wire produces the maximum signal transfer and dampens the ringing of a reflected signal.

If you are using the adapter to interface with one piece of equipment with a short cable run (under 150 feet) in an electrically ‘clean’ environment (like an office) then you probably do not need the cable to be terminated. If on the other hand you are using the ANC-6085 to interface with 2 or more RS-485 devices in an industrial environment with hundreds of feet of cable runs - terminating both ends of the cable at the end points would be required. The adapter has a jumper enabled 120 ohm resister (JP4) that takes care of the adapter end of the cable. The user must connect a similar resister at the far end of the cable run. An unterminated cable will not work generally with long cable runs, and baudrates above 2400 baud. Externally powering the adapter for such an application would certainly be required. The best way to determine if termination is causing your interface not to work is to just enable the ANC-6085 terminating resister and install a 120 ohm resister onto the last piece of RS-485 equipment on the cable. Check also, that you have not over-terminated the cable by having more than two resisters installed. Access one end of the cable and use a multimeter set to the 200 ohm scale. You should measure about 60 ohms if there are two 120 ohm resisters in parallel across the cable. If you are using multiple Antona adapter’s, only one at each end of the cable should have JP4 enabled. Likewise, check any other pieces of equipment on the cable to make sure if they contain termination resisters that only one of them is enabled.

Jumpers

On the ANC-6085/6090, there are three main jumpers - JP1/2/3 that control the operation of the signal switching for transmit and receive enabling. Double check that you have set the jumpers correctly for your application. All three jumpers must be installed for the adapter to work properly and it is possible to have one mis-setting cause the adapter to appear non-operational. Check the adapter jumper settings against the schematic and product user's manual.

Powering

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 RS485/422 piece of equipment you are interfacing to may be over a long cable run and/or terminated with a 120 ohm resister (you can try disconnecting the termination resister also - some types of equipment, like the ANC-6085 and ANC-6090, give you a jumper option for the termination resister), so it might be necessary to externally power the adapter through the RS485/422 side by applying +3v 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 serial 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. For many RS-485 multidrop industrial control applications, the baud rate is much slower, like 9600, no 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.

RS485/422 Equipment

Try to verify the operation of the target equipment independent of the Antona adapter by using another setup - a different cable connected to another RS485/422 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 RS485/422 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, Appendix B in this manual. It is easy to put a scope probe onto the tops of the 4 jumpers (JP5/6) and verify that RS485/422 signals are coming and going to the adapter. Test the +power to the adapter by attaching a probe to the +lead of the 22uf capacitor near the +3v regulator. 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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