Explanation of function codes
Read Coil Status [01h]:
This function reads the status (ON/OFF) of selected coils. An example follows below.
x
Read intelligent input terminals [1] to [5] of an inverter having a slave address “8.”
x
This example assumes the intelligent input terminals have terminal states listed
below.
Item
Data
Intelligent input
terminal
[1]
[2]
[3]
[4]
[5]
Coil number
7
8
9
10
11
Coil Status
ON
OFF
ON
OFF
OFF
Query:
Response:
No.
Field Name
Example
(Hex)
No.
Field Name
Example
(Hex)
1
Slave address *1
08
1
Slave address
08
2
Function code
01
2
Function code
01
3
Coil start address *4
(high order)
00
3
Data size (in bytes)
01
4
Coil start address *4
(low order)
06
4
Coil data *3
05
5
Number of coils
(high order *2)
00
5
CRC-16 (high order)
92
6
Number of coils
(low order *2)
05
6
CRC-16 (low order)
17
7
CRC-16 (high order)
1C
8
CRC-16 (low order)
91
Note 1:
Broadcasting is disabled.
Note 2:
When 0 or more than 31 is specified as a number of coils, error code “03h” is
returned.
Note 3:
Data is transferred by the specified number of data bytes (data size).
Note 4:
The PDU Coils are addressed starting at zero. Therefore coils numbered 1-31
are addressed as 0-30. Coil address value (transmitted on Modbus line) is 1
less than the Coil Number.
x
The data set in the response shows terminal state of coils 7 to 14.
x
Data “05h = 00000101b” indicates the following assuming coil 7 is the LSB.
Item
Data
Coil Number
14
13
12
11
10
9
8
7
Coil Status
OFF
OFF
OFF
OFF
OFF
ON
OFF
ON
x
When a read coil is outside the defined coils, the final coil data to be transmitted
contains “0“as the status of the coil outside the range.
x
When the Read Coil Status command cannot be executed normally, see the exception
response.
B
10
Appe
ndix B
B
−
10
Appendix B
