Omron DEVICENET#05-2003 - Communications Cycle Time and Refresh Time

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Remote I/O Communications Characteristics Section 6-1
Maximum I/O Response Time
The maximum I/O response time occurs with the I/O timing shown in the fol-
lowing diagram.
T
IN
: Input I/O Unit ON (OFF) delay time
T
OUT
: Output I/O Unit ON (OFF) delay time
T
CYCIF
: I/O Unit interface cycle time (see 6-1-3 I/O Unit Interface Cycle Time)
T
RM
: Communications cycle time for the whole network
The maximum I/O response time (T
MAX
) is the total of the following terms:
T
MAX
= T
IN
+ T
CYCIF
× 2 + (DeviceNet I/O response time) + T
OUT
Note For details on the Input I/O Unit input delay time and the Output I/O Unit out-
put delay time, refer to information on the I/O Units in 1-1 MULTIPLE I/O TER-
MINAL; for details on the I/O Unit interface cycle time, refer to 6-1-3 I/O Unit
Interface Cycle Time; for details on the DeviceNet I/O response times, see the
explanation of the remote I/O communications performance.
Note Refer to the PC’s Operation Manual for details on the PC’s cycle time.
6-1-2 Communications Cycle Time and Refresh Time
This section explains the communications cycle time, communications time/
Slave, and refresh time.
Communications Cycle
Time
The communications cycle time is the time from the completion of a Slave’s
remote I/O communications processing until remote I/O communications with
the same Slave are processed again. The communications cycle time is used
to calculate the maximum I/O response time.
The communications cycle time depends on the number of Masters on the
Network and on whether or not message communications are being per-
formed. The explanation given here applies to use with 1 Master. For use with
several Masters, refer to the explanation on remote I/O communications char-
acteristics in DeviceNet Operation Manual (W267).
The following equations show the communications cycle time (T
RM
) when
there is only 1 Master in the Network.
T
RM
= Σ (communications time per Slave: T
RT
)
+multiple Units processing time
+Explicit message processing time
+0.01
× N + 1.0 (ms)
Instruction execu-
tion cycle time
Peripheral serv-
icing cycle time
Peripheral servic-
ing cycle time
DeviceNet Master Unit
DRT1-COM
Communications Unit
DeviceNet I/O response time
Input Unit
Output Unit
PC