10
5.2.2
Read Input Status Response
The data is packed one bit for each input (1 = active, 0 = inactive). The response includes the slave address, function code,
quantity of data characters, the data characters and error checking. The low order bit of the first character contains the first
addressed input and the remainder follow. For input quantities that are not even multiples of eight, the last characters are filled-
in with zeros at high order end.
Example
– the response to the read input status query shows the following:
Digital input A1
–
active
Digital input B1
–
inactive
Digital input B2
–
active
Digital input B3
–
inactive
Digital inputs C1, C2, C3
–
inactive
Digital inputs D1, D2, D3
–
inactive
Digital inputs E1, E2, E3
–
inactive
Digital inputs G1, G2, G3
–
inactive
…5
MODBUS FUNCTIONS
5.3.2
Read Holding 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
contains the high order bits and the second the low order bits.
Example
– the response to the read holding register query shows the following:
Alarm A trip point
–
150
Alarm B trip point
–
50
Alarm C trip point
–
100
Alarm D trip point
–
400
Alarm E trip point
–
0
Alarm F trip point
–
0.
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6
1
-
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R
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(
1
0
3
0
C
0
6
9
0
0
2
3
0
0
4
6
0
0
0
9
1
0
0
0
0
0
0
0
0
0
9
D
1
9
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2
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2
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5
0
0
0
A
B
8
E
5.3
Read Holding Register – Function Code 03
5.3.1
Read Holding Register Query
The Read holding registers allow the user to obtain the binary contents of holding 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
5, the data start register must be set to 50 (32H).
Broadcast mode is not allowed.
Example
– a read holding register request to read 6 holding registers from slave (01) starting at holding address 51 (alarm A trip
point) is shown below.
s
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1
0
3
0
0
0
2
3
0
0
6
0
4
6
7
0
