M340 Modbus command to read input registers

[MKhalifa]

Good evening,

I have a PLC P34 1000 and communicate with a flow converter through modbus rtu . but the data i need to read exist on input registers and the manual of converter telling that you have to use command 4 as known but when i'm using read_var the communication halt after a while and the data is not recognized because the data type sent is floating.

by the way i read the holding registers and everything is ok.

thank you in advance

[RoozeeR · Accepted solution]

The READ_VAR function should be able to read input registers as long as you define the obj type as %IW. The function code to read %IW is 4 .

You mention " the data is not recognized because the data type sent is floating.":

1: does this mean that the input data you read is a 32-bit floating point (real) data? In that case you should adjust the read length to 2 (registers= 32 bits).

2: What is not recognizing the data?