F
Hello
I am currently having issues with a modbus interface that I am testing for a project.
I am trying to read and write data to and from a modbus slave using a GE Fanuc 90-70 PLC using the RTM-700 horner module using 1 SCB and two MCB's configured for functions 03 read holding registers and 16 Preset Multiple Holding Registers.
The configuration of the blocks is limited to the following:
slave address is 1
the command is either 03 or 16
the reference offset is 0 or 500
the length is 233 and 13
and the PLC references and byte type %R
The issue I am having is when it has completed its initialization and is transmitting to the slave simulator I have set up using modbus, it does not seem to transmit any of the configured data. and instead writes a garbage message to the slave of "RX FA F2 FF FF FF 2D AF 37" or "RX FD FE FF FF 2D AF 37" from the PLC and receives a bad CRC error B. this is all that the modbus shows for crc b or g.
So far I have found that this could be caused by either a mismatched Baud rate which I have checked at both ends and is 9600 even RTU 1 stop bit.
A mistake in the wiring which I have checked and found no issues such as tx+ to tx- etc. it is a 4-wire rs485 connection with rx->tx- and rx+>tx+ and ground.
It also seems that pull up/down resistors and shielding might help. but the cable length is only 1m with no sources of interference like motor drives etc to affect the signa.l so I'm not sure if this would have any effect.
If anyone has any suggestions on how to get this working? it would be appreciated as I seem to have run out of ideas.
I am currently having issues with a modbus interface that I am testing for a project.
I am trying to read and write data to and from a modbus slave using a GE Fanuc 90-70 PLC using the RTM-700 horner module using 1 SCB and two MCB's configured for functions 03 read holding registers and 16 Preset Multiple Holding Registers.
The configuration of the blocks is limited to the following:
slave address is 1
the command is either 03 or 16
the reference offset is 0 or 500
the length is 233 and 13
and the PLC references and byte type %R
The issue I am having is when it has completed its initialization and is transmitting to the slave simulator I have set up using modbus, it does not seem to transmit any of the configured data. and instead writes a garbage message to the slave of "RX FA F2 FF FF FF 2D AF 37" or "RX FD FE FF FF 2D AF 37" from the PLC and receives a bad CRC error B. this is all that the modbus shows for crc b or g.
So far I have found that this could be caused by either a mismatched Baud rate which I have checked at both ends and is 9600 even RTU 1 stop bit.
A mistake in the wiring which I have checked and found no issues such as tx+ to tx- etc. it is a 4-wire rs485 connection with rx->tx- and rx+>tx+ and ground.
It also seems that pull up/down resistors and shielding might help. but the cable length is only 1m with no sources of interference like motor drives etc to affect the signa.l so I'm not sure if this would have any effect.
If anyone has any suggestions on how to get this working? it would be appreciated as I seem to have run out of ideas.