CHAPTER 13 RS-485 COMMUNICATIONS
13-22
Modbus RTU Communications
13
Communication CONT/OUT signal
The CONT/OUT signal is divided into two types: the hardware signal (sequence I/O terminal) and the
communications signal (Modbus communications) depending on the I/O form as shown in the table
below. For the hardware CONT/OUT signals, refer to the page of the sequence monitor.
Hardware signal
Communications
signal
CONT signal
CONT1-5 (5 bits) CONT9-24 (16 bits)
OUT signal OUT1-3 (3 bits) OUT6-21 (16 bits)
It is possible to write and read the CONT signals via RS-485 communications. In reading and writing,
the same type of signals (5 to 16 bits) are handled in a batch data.
The following shows the signal arrangement in the data. The signal turns on with the corresponding bit
“1” and off with bit “0”.
a) Communication CONT signal (CONT9 - 24)
00h
00h
CONT24 CONT23CONT22CONT21CONT20CONT19CONT18 CONT17
Data 4bytes
CONT16 CONT15CONT14CONT13CONT12CONT11CONT10 CONT9
b) Communication OUT signal (OUT6 - 21)
00h
00h
OUT21 OUT20 OUT19 OUT18 OUT17 OUT16 OUT15 OUT14
Data
4bytes
OUT13 OUT12 OUT11 OUT10 OUT9 OUT8 OUT7 OUT6
Relation with coil data manipulation
Manipulating CONT/OUT signals can be performed in the following two ways: a batch data operation
(FC 03h, and 10h) by specifying data addresses and individual operation per bit (FC 01h, 05h, and
0Fh) by specifying each coil address. Among these, the signal statuses will follow the latest
manipulation regardless of method of batch data operation or coil address specification for
communication CONT signals 9 to 24 to which data can be written (FC 05h, 0Fh, and 10h).
Sequence monitor
(1) Hardware CONT signal and hardware OUT signal
The CONT signal and the OUT signal of sequence I/O can be loaded.
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