YOKOGAWA UT150L, User Manual

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IM 05C01E22-10E
4-1
Chapter 4 MODBUS Communication
4. MODBUS Communication
4.1 Overview
Maximum overall cable length of 1200 m for a maximum of 31 substations
Personal computer
Figure 4-1 Connection of Slaves in MODBUS Communication
Use of the MODBUS communication enables UT150L to communicate with a wide variety of devices
such as PCs. In this communication, you use such device to read/write data from/into D registers,
(internal registers) of the UT150L.
Hereafter, PCs are generally called “host devices.”
See Also
Chapter 5 for information on the D registers.
For the MODBUS communication of the UT150L, we provide the ASCII mode (ASCII system) and
RTU mode (binary system) for the communication mode.
Table 4-1 ASCII and RTU Modes
Item
Number of data bits
Message start mark
Message end mark
Length of message (Note 1)
Error detection
Note 1: When the length of a message in the RTU mode, it is assumed to be “N.”
Note 2: When the communication rate is 9600 bps, 1
9600 24 sec or less.
Data time intervals
ASCII Mode
7 bits (ASCII)
1 second or less
2N + 1
CR + LF
: (colon)
Longitudinal redundancy check: LRC
24 bit time or less (Note 2)
Not necessary
Not necessary
8 bits (binary)
RTU Mode
N
Cyclic redundancy check: CRC-16
In the MODBUS communication, a higher-level device identifies each UT150L with a communication
address of 1 to 99. Some of the commands used let you specify broadcast that requires no address
numbers. For more information on broadcast specifications, see subsection 4.2.2.