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C-8 Micro PLC Programmer’s Guide – April 1994
GFK-0804B
RTU Message Length
To generate the CRC–16 for any message, the message length must be known. The
length for all types of messages can be determined from the table below.
Function Code And Name
Query or Broadcast
Message Length
Less CRC Code
Response Message
Length Less CRC
Code
0
1
2
3
4
5
6
7
8–14
16
17
18–127
128–255
Read Output Table
Read Input Table
Read Registers
Read Analog Input
Force Single Output
Preset Single Register
Read Exception Status
Loopback/Maintenance
Preset Multiple Registers
Report Device Type
Not Defined
6
6
6
6
6
6
2
Not Defined
7 + 7th byte
1
2
Not Defined
Not Defined
Not Defined
3 + 3rd byte
1
3 + 3rd byte
1
3 + 3rd byte
1
3 + 3rd byte
1
6
6
3
Not Defined
6
8
Not Defined
3
1
The value of this byte is the number of bytes contained in the data being transmitted.