owend
Member
I am looking for a little advice with respect to watchdog timers and MODBUS communication.
We are attempting to use several PM564-ETH (ABB, AC500-eco series PLC)and a CP435T-ETH (ABB, touch screen HMI) to demonstrate MODBUS communication techniques in a mock industrial situation for teaching purposes.
I can achieve communication between the PLCs. Either with both PLCs being MODBUS masters and requesting in information from each other or with one PLC as the master and reading and writing information from the other PLC.
I can also achieve normal master/slave communication between the CP435 HMI when the PLC is does not have any other MODBUS communication tasks.
However as soon as I connect the CP435 HMI panel to a PLC that is also handling PLC to PLC MODBUS communication, I start getting watchdog timeout errors. I have searched the help and scoured the internet for information on adjusting the watchdog but haven’t had any luck. I have played with the “Free wheeling pause” parameter in the CPU configuration think it might be the watchdog adjustment but even extending it from the default 10ms to 255ms doesn’t solve the issue.
Is there a way of adjusting the watchdog time and cycle time to avoid this or turning the watch dog off altogether?
Or some other way around this issue? (i.e. am I doing something wrong)
I realise that disabling/extending watchdog timers has serious implications for system safety, but for demonstration purposes I can’t see this being an issue. I am assuming the watchdog timer is going off because the CPU is to slow to handle multiple MODBUS operations.
Any light you kind people here can shed on the subject would be great.
Kind Regards
Dylan Owen
We are attempting to use several PM564-ETH (ABB, AC500-eco series PLC)and a CP435T-ETH (ABB, touch screen HMI) to demonstrate MODBUS communication techniques in a mock industrial situation for teaching purposes.
I can achieve communication between the PLCs. Either with both PLCs being MODBUS masters and requesting in information from each other or with one PLC as the master and reading and writing information from the other PLC.
I can also achieve normal master/slave communication between the CP435 HMI when the PLC is does not have any other MODBUS communication tasks.
However as soon as I connect the CP435 HMI panel to a PLC that is also handling PLC to PLC MODBUS communication, I start getting watchdog timeout errors. I have searched the help and scoured the internet for information on adjusting the watchdog but haven’t had any luck. I have played with the “Free wheeling pause” parameter in the CPU configuration think it might be the watchdog adjustment but even extending it from the default 10ms to 255ms doesn’t solve the issue.
Is there a way of adjusting the watchdog time and cycle time to avoid this or turning the watch dog off altogether?
Or some other way around this issue? (i.e. am I doing something wrong)
I realise that disabling/extending watchdog timers has serious implications for system safety, but for demonstration purposes I can’t see this being an issue. I am assuming the watchdog timer is going off because the CPU is to slow to handle multiple MODBUS operations.
Any light you kind people here can shed on the subject would be great.
Kind Regards
Dylan Owen
