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Hi, I’m new to the forum and quite new to the Modbus protocol and I'm hoping someone can help me with my Modbus problem.
I am using RS485 to communicate with a generator engine controller. The controller stores a series of event records across several string type registers that contain firstly date, time and event log reason; secondly the state of all inputs/outputs of the engine (this works well and is not the issue).
The issue is:
To acquire this data I must first write to a 16-bit signed register the actual ID of the event record before I can read out the data. The record ID's range from 0 to approx. -1200 depending on the records logged. I have had success writing from 0 to -128 and the correct records are then contained in the appropriate registers but after -128 I have many problems, for example: When trying to write -384 I am actually given record -128 but -385 is ok and gives me the correct record. And again writing -256 give me -256 but -257 gives me -1. I have looked at the binary values etc. and cannot see a problem.
Any help is greatly appreciated!
I am using RS485 to communicate with a generator engine controller. The controller stores a series of event records across several string type registers that contain firstly date, time and event log reason; secondly the state of all inputs/outputs of the engine (this works well and is not the issue).
The issue is:
To acquire this data I must first write to a 16-bit signed register the actual ID of the event record before I can read out the data. The record ID's range from 0 to approx. -1200 depending on the records logged. I have had success writing from 0 to -128 and the correct records are then contained in the appropriate registers but after -128 I have many problems, for example: When trying to write -384 I am actually given record -128 but -385 is ok and gives me the correct record. And again writing -256 give me -256 but -257 gives me -1. I have looked at the binary values etc. and cannot see a problem.
Any help is greatly appreciated!