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A.2. Net ID (Station Number)
The first byte in the frame structure of a Modbus RTU query is the receiver's address. Availed
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.
A.3. 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 be set to '1' if an error occurs in the system. In this way,
the master will know whether the message has been transmitted correctly or not.
Code
Function
Read the Status of the Coils (Readback DOs)
0x01
Read the Status of the Input(Reads DIs)
0x02
Read the Holding Registers (Readback AOs)
0x03
Read the Input Registers (Reads AIs)
0x04
Force a Single Coil (Writes DO)
0x05
Preset a Single Register (Writes AO)
0x06
Force Multiple Coils (Writes DOs)
0x0F
Preset Multiple Registers (Writes AOs)
0x10
PET-AR400 User Manual
V1.0.0
Reference
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