7-1
Section
Overview of Message Communications
84
7-1
Overview of Message Communications
Explicit messages can be sent between nodes in a DeviceNet network to trans-
fer data and control other nodes.
The DeviceNet Interface Unit can freely write the contents of PT memory from
the Master using DeviceNet explicit messages. This function allows PT memory
outside of the allocated input and output areas to be accessed from the host to
control the PT or read its status.
7-1-1 Exchanging Data with the DeviceNet Interface Unit
Data can be exchanged between the host (Master) and a DeviceNet Interface
Unit using message communications to control the PT or read its status.
PT data (control/notify areas, elements, etc.) must be allocated to PT memory to
enable explicit message communications from the Master (PC) to the PT via the
DeviceNet Interface Unit. (The allocation method is the same as a regular link
method.)
IOWR
CMND
or
Master Unit
PC
Send an explicit message command
with an IOWR or CMND instruction
to read or write PT memory.
Explicit messages
Response
Command
PT
Elements
Allocation
PT memory
within the PT
All areas
can be
read/written
DeviceNet Interface Unit
Elements on the PT screen
can be directly accessed
using PT memory.
The command from the Master (host) is
interpreted, data is read from (written to)
the specified location in PT memory,
and the read data (command result) is
returned as a response.
Reference 1. Use the EXPLICIT MESSAGE SEND (28 01) FINS command when send-
ing an explicit message from an OMRON Master Unit.
With CVM1/CV-series PCs, send FINS commands with the CMND instruc-
tion. With CS1-series or C200HX/HG/HE PCs, send FINS commands with
the IOWR instruction.
2. Explicit messages cannot be sent when a C200HS is used as the Master.
(Data can only be read and written with remote I/O communications.)
7-1-2 Data Flow of Explicit Messages
When sending an explicit message, execute the CMND or IOWR instruction in
the ladder program to send the EXPLICIT MESSAGE SEND (28 01) FINS com-
mand to the DeviceNet Master Unit in the local node.
The Master Unit removes the FINS header from the received FINS command,
converts the command to an explicit message, and transmits it to the destination
Slave (PT).