ICP DAS USA ET-2242 User Manual page 74

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ET-2200 Series Ethernet I/O Modules

RTU Data Structure
Byte 06
Net ID
(Station Number)

Net ID specifies the address of the receiver (Modbus/TCP slave).

Function Code specifies the message type.

Data Field is the data block.
Net ID (Station Number)
The first byte in the frame structure of a Modbus RTU query is the re ei er s address. A valid
address is in the range of 0 to 247. Address 0 is used for general broadcast, while addresses 1 to 247
are given to individual Modbus devices.
Function Code
The second byte in the frame structure of a Modbus RTU query is the function code, which
describes what the slave device is required to do. Valid function codes are between 1 and 255. To
answer the query, the slave device uses the same function code as contained in the request. The
highest bit of the function code will only e set to
the master will know whether the message has been transmitted correctly or not.
Section Code
6.2.1 01 (0x01)
02 (0x02)
6.2.2
6.2.3 03 (0x03)
6.2.4 04 (0x04)
05 (0x05)
6.2.5
6.2.6 06 (0x06)
6.2.7 15 (0x0F)
6.2.8 16 (0x10)
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Byte 07
Function Code
Reference Number
(Address Mapping)
Read the Status of the Coils (Readback DOs)
Read the Status of the Input (Reads DIs)
Read the Holding Registers (Readback AOs)
Read the Input Registers (Reads AIs)
Force a Single Coil (Writes DO)
Preset a Single Register (Writes AO)
Force Multiple Coils (Writes DOs)
Preset Multiple Registers (Writes AOs)
Bytes 08 - 09
Data Field
if an error occurs in the system. In this way,
Function
Bytes 10 - 11
Number of Points
Reference
(Address)
0xxxx
1xxxx
4xxxx
3xxxx
0xxxx
4xxxx
0xxxx
4xxxx
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