Ethernet I/O Modules
6.2.4 04 (0x04) Read the Input Registers (Read AIs)
This function code is used to read either the input registers or the current analog input value from the
PETL/tET/tPET module.
These registers are also used to store the current value for the digital counter, the number of DI
channels and the number of DO channels, etc.
[Request]
Byte
Description
Size
Value
00
Net ID (Station Number)
1 Byte
1 to 247
01
Function Code
1 Byte
0x04
02-03
Starting AI Address
2 Bytes
Refer to the Modbus Address Table for the
PETL/tET/tPET series.
(
Section 6.3 Modbus Register Table
Byte 02 = high byte
Byte 03 = low byte
04-05
Number of 16-bit Registers
(Channels)
2 Bytes
Word Count
Byte 04 = high byte
Byte 05 = low byte
[Response]
Byte
Description
Size
Value
00
Net ID (Station Number)
1 Byte
1 to 247
01
Function Code
1 Byte
0x04
02
Byte Count
1 Byte
Byte Count of the Response (n=Points x 2 Bytes)
03~
Register Values
n Bytes
Register Values
n= 2; Byte 03 = high byte
Byte 04 = low byte
.......
n= m; Byte 03 = high byte
Byte 04 = low byte
.......
Byte m+1 = high byte
Byte m+2 = low byte
[Error Response]
Byte
Description
Size
Value
00
Net ID (Station Number)
1 Byte
1 to 247
01
Function Code
1 Byte
0x84
02
Exception Code
1 Byte
Refer to the Modbus Standard Specifications for
more details.
ICP DAS CO., LTD.
PETL/tET/tPET DIO Series User Manual, Ver. 2.1, Sep. 2014, Page: 86
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