ICP DAS USA ET-2242, User Manual

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ET-2200 Series Ethernet I/O Modules
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6.2.3 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 ET-2200 series 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 ( Section 6.3
Mod us ‘egister
Table ) for the ET-2200 series
module.
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
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