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Change Baud Rate on RS485 Port After Boot?


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I know that the Baud Rate for the CPU's RS485 Port (along with the Data Bits, Stop Bits, and Parity) are set in the configuration prior to downloading the program.

I  have the RS485 CPU COM Port set this way as MODBUS Master and have successfully communicated with Alicat MFC's via Modbus with little effort (yay to UniLogic/UniStream).

However, when I change baud rate for an item on in the Physical Serial COM configuration it is applied to the entire bus and I don't see away to reconfigure it.

I would like to be able to change the baud rate without rebooting or loading another program. I am aware it might be possible by using entries in the *.ini file on the SD card, but I think the PLC will need to be booted each baud change for that to work. As I recall you are allowed to load one and only one config file per boot.

Is there a way to change Baud Rate on RS485 Port and other parameters from the ladder logic or another way without rebooting.

I have a work around, but I was surprised that there was not an obvious way to initialized the com port from the ladder.

Specifically I am using an USP-104-B10 with the USC-P-B10 CPU and Modbus RTU at 9600 & 57,600 Baud. I need to initialize some hardware and was hoping I could just program the PLC to do it as needed. The default baud rate is not fast enough for normal communication so that and its default ID need to be changed each time a new piece of hardware enters the system.

In the past I have used an ICP DAS module to share  a single bus with a variety of equipment operating at different baud rates with different parity and a variety of protocols also to give each an ID on the bus. The I-7527 addressable gateway works great for that when you need to deal with that kind of situation long term.

This time everything is going to be Modbus and I plan to run at 57,600 baud after configuration.

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