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Appendix A
DeviceNet Overview
© National Instruments Corporation
A-9
slave. This strobe command (request) message is received by all slave
devices simultaneously and can be used to trigger simultaneous
measurements (such as to take multiple photoelectric readings
simultaneously).
devices simultaneously and can be used to trigger simultaneous
measurements (such as to take multiple photoelectric readings
simultaneously).
When a strobed slave receives the strobe command, it uses the output data
bit that corresponds to its own MAC ID (for example, the slave with
MAC ID 5 uses bit 5). Regardless of the value of its output bit, each
strobed slave responds to the command message by sending an individual
strobe message back to the master. The slave’s strobe response contains
from 0 to 8 bytes of input data.
bit that corresponds to its own MAC ID (for example, the slave with
MAC ID 5 uses bit 5). Regardless of the value of its output bit, each
strobed slave responds to the command message by sending an individual
strobe message back to the master. The slave’s strobe response contains
from 0 to 8 bytes of input data.
Figure A-4 shows an example of four strobed slave devices.
Figure A-4. Strobed I/O Example
Change-of-State and Cyclic I/O
The change-of-state (COS) and cyclic I/O connections both use the same
underlying communication mechanisms. Both transmit data at a fixed
interval called the expected packet rate (EPR). Since COS and cyclic
I/O connections use the same messaging on the DeviceNet network, they
are often referred to as a single I/O connection called COS/cyclic I/O.
underlying communication mechanisms. Both transmit data at a fixed
interval called the expected packet rate (EPR). Since COS and cyclic
I/O connections use the same messaging on the DeviceNet network, they
are often referred to as a single I/O connection called COS/cyclic I/O.
Master
MAC ID = 1
Slave
MAC ID = 9
Slave
MAC ID = 11
Slave
MAC ID = 12
Slave
MAC ID = 13
6 Byte Strobe
Response
2 Byte Strobe
Response
1 Byte Strobe Response
4 Byte Strobe Response
0
1
2
9 10 11 12 13
61 62 63
8 Byte Strobe Command
Used
by 9
Used
by 11
Used
by 12
Used
by 13
Output data
Input data