7-2
Section
Using Message Communications
97
The unit address of the local Master Unit is not between 0 and F, the Master
Unit is mounted on a Slave Rack, etc.
2. The behavior of the Message Communications Enabled Flag in CVM1 and
CV-series PCs is different from the behavior in CS1-series and C200HX/
HG/HE PCs.
3. With CS1-series PCs, there are no memory addresses for the Equals Flag
and the Error Flag.
Timing the Reading of Responses
When reading the response from the DeviceNet Interface Unit after execution of
IOWR, read the response in the cycle after the one in which IOWR is executed
and when the Message Communications Enabled Flag is ON.
Even if IOWR execution is finished, the status of the Message Communications
Enabled Flag will not change until the next peripheral servicing in the CPU Unit.
If the response is returned in the same cycle as IOWR execution, the Message
Communications Enabled Flag will remain ON. If the response is not received
until the next cycle, the Flag will turn OFF during peripheral servicing and then
turn ON at the next peripheral servicing after the response is received.
If the Message Communications Enabled Flag is used in the same cycle as the
execution condition for reading the response after execution of IOWR, an at-
tempt could be made to read the response even though it has not yet been re-
turned.
Response Received in the Same Cycle
CPU Unit
IOWR
executed
Command
written
Master Unit
Message
Response
: Peripheral servicing
Equals Flag (SR 25506)
Message
Communications
Enabled Flag
Response
read
Response Received in the Next Cycle
CPU Unit
IOWR
executed
Command
written
Master Unit
Response
: Peripheral servicing
Equals Flag (SR 25506)
Message
Communications
Enabled Flag
Response read
OFF until response is
received
Message Communications
Enabled Flag remains ON
here.
Message