Devicenet Connections - Omron CJ1W-DRM21 Operation Manual

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DeviceNet Connections

DeviceNet has several different protocols for remote I/O communications between Master and Slave
devices. Connections are units used to manage those protocols.
There are four kinds of DeviceNet remote I/O communications protocols (connections): Poll, bit–strobe,
COS (change of state), and cyclic. CJ-series DeviceNet Units support all four types.
The connection used by the DeviceNet Unit is automatically selected if the CX-Integrator is not used. If
you use the CX-Integrator, you can automatically select the connection by the DeviceNet Unit, or you
can specify the connections for each slave. You can set up to two connections. COS and cyclic connec-
tions cannot be specified at the same time.
Note If you use COS and cyclic connections, do not connect multiple Master Units on one network.
The characteristics of each connection are outlined in the following table.
Connection
Poll Used for basic I/O.
Bit-strobe Used for input of 8 bytes or less. Sends broadcasting requests from master and receives input
from slaves.
COS (Change of Communications occur at regular cycles (heartbeat timer) and the con-
State) nection is determined by the master or slave sending the data.
You can send data only when required, which reduces the network com-
munications load.
You can use this connection to send data to the master or slave if the
master or slave data changes.
COS connections are given priority over poll and bit-strobe connections,
which may result in a longer communications cycle time due to the
higher frequency of COS connections used to send data or large
amounts of data sent with the use of COS. Therefore, COS connections
are effective when changes to data are infrequent (approximately 100
ms min.), or to give higher priority to small amounts of data.
For DeviceNet Units, you can decide the transmission timing in the user
program.
The following points apply for CJ-series DeviceNet Units:
If the master *_MstrCOSSendCmd (Master COS Send Switch) is
changed to TRUE, remote I/O communications output data can be sent
every time from the master using COS to the slaves that support COS.
If *_Sw2SlavCOSSendCmd (Slave COS Send Switch) is set to TRUE,
you can send remote I/O communications output data every time from
the slave using COS to the master (input data from the perspective of
the master).
Even if the software switch is not changed to TRUE, you can perform
the COS communications using regular cycles (heartbeat timer) simul-
taneously.
Note This CJ-series DeviceNet Unit supports COS.
Cyclic Communications timing is determined by regular cycles (heartbeat
timer).
Masters and slaves send output or input data in regular cycles.
Cyclic connections are have higher priority than poll or bit-strobe con-
nections, which may result in a longer communications cycle time due
to large amounts of data sent with the use of cyclic connections. There-
fore, cyclic connections are effective when changes to data are infre-
quent, or the amount of data to be sent is small.
CJ-series DeviceNet Units Operation Manual for NJ-series CPU Unit(W497)
Characteristics
Appendices
Note COS and cyclic
connections
cannot be used
at the same
time.
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