SB 236 indicates that there is an error in the CANbus network.
SI 236 CANbus Network: Failed Unit ID. Note that the first 3 bits turn ON only when the controller is unable to broadcast via the CANbus port. The value of SI 236 indicates the following messages:
Value |
Message |
May result from: |
0 |
No Acknowledgement |
CANbus power failure, crossed wires, incorrectly set termination points. |
1 |
CANbus OFF
|
|
2 |
CANbus Warning error
|
Poor transmission quality due to faulty wiring, or if the cable length exceeds recommendations. |
4 |
One or more networked units cannot be read. If this bit is ON, check SI 238, SI 240-243. |
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SI 237 CANbus Network Communication Error Code is a bitmap that indicates the LAST unit that cannot be read. Note that each controller can receive messages from up to 8 others. Example: Assume that there are 6 controllers in the network (3,6,8,13,17,34). Controller 3 is waiting for data from controllers 8 and 13 and 17. If the controller does not receive data from controller 13 (assume a 1 second timeout) then SI 237 will contain a value of 13. Bit 4 in SI 236 will also turn ON. Once controller 3 has received the data, Bit 4 turns OFF.
SIs 240, 241, 242, and 243 serve as a bitmap indicating which unit is in error. If, for example, the network includes unit ID numbers 8, 9 and 13, and PLC #9 cannot be accessed, then the ninth bit in SI 240 will turn ON. When the error is fixed, the bit falls to OFF.
Problem |
Possible cause |
Recommended Action |
Failed communication |
Baud rate settings |
All M90's in the network must be set to the same CANbus baud rate. These may be edited in the M90 OPLC Advanced settings. |
|
Termination resistors |
Check the M90 user guide for details. |
|
CANbus power supply |
Check that the CANbus power supply is properly connected, and that the voltage is in the permissible range as described in the M90 User Guide. |
|
Incorrect ID number |
You may not have assigned the correct unit ID number in your operand addresses (between 1-63). Check in the M90 OPLC settings. |
PC cannot communicate with bridge |
Incorrect ID number |
When you communicate with the M90 unit that you are using as a bridge to the network, select Unit ID number 0, or select Stand-alone project in the M90 OPLC settings. |
PC cannot communicate with network |
Communication settings |
If you are trying to communicate with an M90 network via a bridge, you must define your project as a Network project--however, U90 Ladder cannot automatically detect communication settings in a Network project. Make sure the current RS232 parameters in your project are the same as the parameters that are actually in the bridge. |
|
Incorrect baud rate |
The bridge's RS232 port's baud rate cannot be set below 9600. |