I have a USR DR302 rs485 to tcp gateway(converter).
I connect it to ignition using the Modbus TCP driver but noticed that when I try to request tag data for more than two slaves it starts giving me bad tag value and timeout error. If I poll one slave at a time it works perfectly.
Has anyone come across this issue before ?
Make sure concurrency is set to one for such devices.
Yes , It is set to one. And same issues persists
Just looked up the USR DR302. From the Amazon description, it isn't a modbus gateway. It is simply a serial rs485 to ethernet gateway. That means it needs the Modbus RTU over TCP driver, not the Modbus TCP driver.
IA's modbus RTU driver doesn't even try to enforce any RTU timing specs. You may need either a true MB Gateway device, or possibly my alternate driver.
It does have option where you tick Modbus RTU to TCP. I ticked that as well so it could convert properly. Only issue is when I try to poll more than 1 slave, it throws the readinput register timeout errors.
Perhaps that option simply doesn't work. There's a review on Amazon from someone unsuccessfully trying Modbus TCP and getting no help from USR. I would presume USR is confused by the difference between Modbus RTU Over TCP and Modbus TCP. Or simple incompetence.
So what can I do in this case? The client already installed them
Reconfigure to the Modbus RTU over TCP driver, and turn off the device's Modbus TCP function.
Meanwhile, you should also verify that your devices on the RS485 bus are compatible with each other. Enable tags for the different units one at a time, to ensure each one functions correctly when it is the only one responding. Then try the various combinations of units together, to see if there's any clashes.
A wireshark capture in concert with a serial line snooper may also help.
Thank you. I will try these