Ethernet I/O Modules
ICP DAS CO., LTD.
PETL/tET/tPET DIO Series User Manual, Ver. 2.2, Aug. 2017, Page: 92
03(0x03) Read the Holding Registers (Readback AOs)
This function code is used to readback either the current values in the holding registers or the analog
output value from the PETL/tET/tPET module. These registers are also used to store the preset values
for the digital counter, the host watchdog timer, the module name and the TCP timeout, etc.
[Request]
Byte
Description
Size
Value
00
Net ID (Station Number)
1 Byte
1 to 247
01
Function Code
1 Byte
0x03
02-03
Starting AO 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
0x03
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
0x83
02
Exception Code
1 Byte
Refer to the Modbus Standard Specifications for
more details
