We are currently working on a project where we have to communicate with 3 x Inverters (in parallel mode) and the requirement is to send a Broadcast message to all inverters and perform the function in all inverters at the same time, For example, we would like to set the Operating Mode of all inverters to Auto by sending one message. Modbus broadcast address is 0 as we understand and the problem is that the broadcast message is not performing in this configuration. We are able to set the Mode in each inverter by addressing them directly, with the current wiring in place. Appreciate if someone could advice as to whether there is a different message format for broadcast messages, that is different to Query message that is sent to each Inverter?

 

Except for the slave address in the message being 0x00 making it a Broadcast message, the Broadcast message is formatted the same for whatever function code is being broadcast.

I recall that the Modbus spec says all devices must support broadcast mode, but I also recall reports that broadcast support is vendor/model specific as to whether the 'write' function codes support broadcast, for example, https://control.com/forums/threads/modbus-broadcast-via-egx100mg.34898/ Which means that the broadcast function is vendor/model specific.

The single loop PID controller's manual that I'm working with shows that these three commands are supported in Broadcast mode:-
- Function Code 05 (force single coil)
- Function Code 06 (Preset/Write single register)
- Function Code 16 (10h) (Preset/Write multiple registers)

 

Except for the slave address in the message being 0x00 making it a Broadcast message, the Broadcast message is formatted the same for whatever function code is being broadcast.

I recall that the Modbus spec says all devices must support broadcast mode, but I also recall reports that broadcast support is vendor/model specific as to whether the 'write' function codes support broadcast, for example, https://control.com/forums/threads/modbus-broadcast-via-egx100mg.34898/ Which means that the broadcast function is vendor/model specific.

The single loop PID controller's manual that I'm working with show that these three commands are supported in Broadcast mode:-
- Function Code 05 (force single coil)
- Function Code 06 (Preset/Write single register)
- Function Code 16 (10h) (Preset/Write multiple registers)

Thanks for the information. I think, this issue is related to the product i.e the Inverter we are using and may be, their firmware does not allow broadcast messaging. As you have pointed out, some devices do not facilitate all Modbus functionality. I will take this matter up with the Inverter manufacturer, although I doubt very much that I will be successful in resolving the problem. Thanks a lot for your help and advice.