Framing
Address Function Data Check
8-Bits 8-Bits N x 8-Bits 16-Bits
Table4.1 Data Frame Format
Address Field
The address field of a message frame contains eight bits. Valid slave device
addresses are in the range of 0~247 decimal. A master addresses a slave by
placing the slave address in the address field of the message. When the slave
sends its response, it places its own address in this address field of the response
to let the master know which slave is responding.
Function Field
The function code field of a message frame contains eight bits. Valid codes
are in the range of 1~255 decimal. When a message is sent from a master to a
slave device the function code field tells the slave what kind of action to perform.
Code Meaning Action
01 Read Relay output Status Obtain current status of Relay Output
02 Read Digital Input (DI) Status Obtain current status of Digital Input
03 Read Data Obtain current binary value in one
or more registers
05 Control Relay Output Force Relay to a state of on or off
16 Preset Multiple-Registers Place specific binary values into a series
of consecutive Multiple-Registers
Table4.2 Function Code
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