Goals and Symptoms
The purpose of this Resolution is to provide the customer with a document to address Modbus connectivity issues
using ProWORX32.
Facts and Changes
The following table shows causes and actions to take to alleviate Exception Error 91 in ProWORX32.
Causes and Fixes
| Cause or Symptom | Action |
| 1. Com port is attached by another program. | Disable or uninstall program attached to com port. Common programs that attach com ports are RSLinx, and HotSync Manager |
| 2. Communication Parameters are incorrect. | Default com parameters are: Address - 1 Protocol - Modbus I Mode - RTU Data Bits - 8 Parity - Even Stop Bits - 1 Baud - 9600 |
| 3. Windows port settings need to be adjusted. | Open Device Manager Click on Ports Click on Com1 Click on Properties Click on Advanced Verify the "transmit and receive buffers" are set to maximum. Verify the FIFO or XON/XOFF box has a check in it. |
| 4. Cable Pinout is incorrect or has a broken wire. Desktop computers programming 9-pin Modbus RS232 port PLCs. | Quantum Programming Cable 990NAA26320 - 12 ft Quantum Programming Cable 990NAA26350 - 50 ft. Compact Programming Cable AS-W952-12 - 12 ft Momentum with 9 pin Modbus connectors can use any of the above. |
| 5. Cable Pinout is incorrect. Laptop computers programming 9-pin Modbus RS232 port PLC. | Alternate jumpered pinout. Note DTR and DSR are jumpered out. This ties handshaking high so a laptop com port with lower voltage can connect to our PLCs. |
| 6. Cable pinout is incorrect or has a broken wire. Desktop computers with RJ45 Modbus RS232 PLC ports. PLCs with RJ45 Modbus programming ports are Compact, Momentum, and the Modicon Micro. | You need to purchase a prewired kit adapter to build this pinout. RJ45 to 9-pin Adapter 110XCA20300 RJ45 Programming Cable 110XCA2820x where x = 1, 3 ft 2, 10 ft 3, 20 ft |
| 7. Cable pinout is incorrect. Laptop computers with RJ45 Modbus RS232 PLC ports. PLCs with RJ45 Modbus programming ports are Compact, Momentum, and the Modicon Micro. | See programming cable part numbers in previous step. RJ45 to 9-pin Adapter - 110XCA20301 The adapter kit for this configuration is NOT prewired. Alternate jumpered pinout. Note DTR and DSR are jumpered out. This ties handshaking high so a laptop com port with lower voltage can connect to our PLCs. |
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