11
5
MODBUS FUNCTIONS…
5.4
Read Input Register – Function Code 04
5.4.1
Read Input Register Query
The read input registers allow the user to obtain the binary contents of input registers in the addressed slave.
Note. The data start register must contain the offset address of the first register to be accessed, e.g. to start at register
01, the data start register must be set to 00.
Broadcast mode is not allowed.
Example
– a read input register request to read 6 input registers from slave (01) starting at input address 01 (A1 analog input) is
shown below.
5.4.2
Read Input Register Response
The addressed slave responds with its address and function code, followed by the information field. The information field contains
1 byte describing the quantity of data bytes to be returned. The contents of each register requested is two bytes, the first byte
includes the high order bits and the second the low order bits.
Example
– with an input range of 0 to 1000mV, the response to the read input register query shows the following:
A1 analog input
– 200
A2 analog input
– 200
A3 analog input
– 200
A4 analog input
– 200
A5 analog input
– 200
A6 analog input
– 200.
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