8-6
Chapter 8. Modbus COMMUNICATION FUNCTION
• 1-frame end judgment
A message end (1-frame end) is determined when a time period specified for
each transmission speed has passed during which no character is received. It is
considered that 1 frame has ended when the next character is not received before
the time-out time shown below passes.
However, the time-out time has a fluctuation of ±1ms from the values in the table
below.
Set transmission speed
(bps)
Time-out time
4800 16ms or more
9600 8ms or more
19200 4ms or more
38400 2ms or more
Command type
There are two command (send message) types as shown below.
Command Description
ASCII RTU (binary)
Read command "03" (sample) 03H (sample)
Write command "10" (sample) 10H (sample)
Other specifications
• Supporting the Modbus Class 0
• Abnormal termination codes
Code Description
01 Command error
02 Address error
03 Data error
• Maximum number of communication data words
Command Number of data
ASCII RTU
03 (READ) 16 16
10 (WRITE) 16 16
• The others
For the details of Modbus specifications,
OPEN Modbus/TCP SPECIFICATION (Release 1.0) by Modicon Inc.
To Next Page
Loading...
