IAI RoboNet Operation Manual page 133

(4) Message Frame
Query and response messages use the following message frame.
Header
T1-T2-T3-T4
* "T1-T2-T3-T4" represents a silent interval.
[1] Header field
The frame starts with a silent interval of 3.5 characters or more.
[2] Address field
The address in the message frame. Fixed to 3FH for the RS485 SIO gateway.
[3] Function field
The following three functions can be used in the Modbus gateway mode.
Code (Hex)
03H Read Holding Registers
06H Preset Single Register
10H Preset Multiple Registers
[4] Data field
This field is used to append data relating to the function code. The data field has a variable length and it can be
omitted.
[5] Error check field
16-bit data is indicated by two bytes of eight-bit data.
The error check result is calculated by the method called "CRC (Cyclical Redundancy Check)."
[6] Trailer field
The frame ends with a silent interval of 3.5 characters or more.
Address Function
8 bits 8 bits
Name
Read holding registers
Write holding register
Write multiple holding registers simultaneously
Part 1 Specification
Data Error check
N x 8 bits 16 bits
Function
Trailer
T1-T2-T3-T4
Broadcast
support
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