Chapter 6 Modbus RTU protocol
57
6.4 Read input memory
(
Func 04-04H
)
Read binary data from the input memory of slave device (refer to 3X state)
。
1. Inquiry (master side)
Slave
address
Functio
n
Initial address
Data quantity
Error check
(CRC16)
High
Low
High
Low
Low
High
1Byte
1Byte
1Byte
1Byte
1Byte
1Byte
1Byte
1Byte
CRC16
2. Answer(slave side)
Slave
address
Functio
n
Number
of bytes
Data
Data
Data
Error check
(CRC16)
Low
High
1Byte
1Byte
1Byte
1Byte
1Byte
1Byte
1Byte
1Byte
CRC16
For example
:
The master side reads the values of the two input memories 300001 (0000H) to 300002
(0001H) from the slave side (address 17).
Inquiry (master side)
Slave
address
Functio
n
Initial address
Data quantity
Error check
(CRC16)
High
Low
High
Low
Low
High
11 H
04 H
00 H
00 H
00 H
02 H
** H
** H
If the values of the slave side 300001 (0000H) ~ 300002 (0001H) are "10 (A H)" and "20
(14 H)", respectively.
Answer (slave side)
Slave
addres
Functio
n
Numbe
r of
Data
Data
Error
check(CRC16)