ICP DAS USA iNS-308, User Manual, Page: 38 / 46

iNS-308 User Manual
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7.2.3 03(0x03) Read the Holding Registers
(Read AO Readback values )
This function code is used to readback either the current values in the holding registers or the Analog
Output value from the iNS-308. These registers are also used to store the preset valuesfor 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 Byte
Byte 02 = high byte
Byte 03 = Low byte
04-05
Number of Registers
(Channels)
2 Byte
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 Byte )
03 Register Values n Byte
n= 1; Byte 03 = high byte
n= 2; Byte 04 = Low byte
.......
n= m; 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