Commands
2014-
02
31
Alternative response: No data carrier in front of the read head.
7.7
Communication via MODBUS TCP/IP
7.7.1
Data exchange via MODBUS TCP/IP
The MODBUS protocol is a simple communication protocol developed in 1979 by Modicon and
used to establish master/slave connections between intelligent devices. The MODBUS
protocol is an open
“
de facto standard
”
and a widely accepted network protocol in industrial
environments.
A MODBUS
master
(controller) and a MODBUS
slave
(IDENTControl Compact) exchange
data by reading and writing registers. The slave contains read and write registers. The master
initiates the data exchange and transfers a command to the write register. The master can then
retrieve the response from the read registers. The terms "input register" and "output register"
are defined from a PLC perspective.
The commands
read holding registers
,
write multiple registers
and
read/write multiple
registers
are available on the IDENTControl Compact for data exchange.
MODBUS communication occurs via port 502. The identification commands correspond to the
commands for communication via TCP/IP.
Visit the website of the Modbus Group at www.modbus.org for information on MODBUS
7.7.2
Registers
Multimaster capability
The IDENTControl Compact can communicate with several masters. Each ident channel can
be addressed by two masters. The first master is the controlling master and addresses the
device using device ID 1. This master possesses both write and read permissions. The second
master is a protocolling master that is able to read the data. The protocolling master addresses
the device using device ID 2. The IDENTControl Compact can be addressed once on each
channel using device ID 1 and once using device ID 2. If another master attempts to address
the device on the same channel, the IDENTControl Compact denies access to this channel. A
maximum of six masters can communicate with the device at any one time.
MODBUS commands
The device supports the commands
read holding registers
,
write multiple registers
and
read/write multiple registers
.
Division of the register
The IDENTControl Compact has two ident channels and a configuration channel. Each
channel is assigned a separate register area so that a different master can address each
channel. All channels can also be addressed by the same master.
Each channel is assigned a register area containing three register groups:
■
Group 1: Output register (device ID 1)
■
Group 2: FIFO input register (device ID 1)
■
Group 3: FIFO monitor register (device ID 2)
00:06:10:02:05:02
00:06
Telegram length (6 bytes)
10
Repeat command code (SR)
02
Word number (2) / Channel (1), toggle bit (0)
05
Status 5 (no data carrier in the detection range)
02
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