Omron DRT2 SERIES DEVICENET SLAVES - OPERATION MANUAL 04-2008 Operation Manual page 470

Remote I/O Communications Characteristics
Maximum I/O Response
Time
PLC
Master Unit
Input
Output
T
8-1-2 Communications Cycle Time and Refresh Time
Communications
Cycle Time
The maximum I/O response time occurs with the I/O timing shown in the fol-
lowing diagram.
Instruction
execution
T T
IN RM
T : The Input Slave's ON (OFF) delay
IN
T : The Output Slave's ON (OFF) delay
OUT
T : The whole Network's communications cycle time (Refer to
RM
page 450.)
T : The PLC's cycle time
PLC
T : The PLC's DeviceNet Unit refresh time (Refer to page 451.)
RF
Note Refer to SECTION 5 General-purpose Slaves and SECTION 6 Environment-
resistive Slaves for details on Input and Output Slaves' ON and OFF delay
times. Refer to Refresh Time on page 451 and the Operation Manual for the
PLC being used for details on the PLC's cycle time.
The maximum I/O response time (T
T = T + 2 × T
MAX IN
The communications cycle time, communications time for each Slave, and
refresh time are explained in this section. All of these times are necessary for
calculating the time required for various processes in a DeviceNet Network.
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 also
used to calculate the maximum I/O response time.
The communications cycle time depends on several factors, including the
number of Masters on the Network and on whether or not message communi-
cations are being per-formed. The following examples provide equations for
when there is only one Master Unit. For details on cycle time equations for
multiple Master Units, refer to page 451.
The following equations show the communications cycle time (T
there is only one Master in the Network.
Even if the equation result is less than 2 ms, the minimum communications
cycle time (T
RM
Instruction
execution
T
PLC PLC
MAX
+ 2 × T + T
RM PLC RF
) is 2 ms.
Instruction
execution
T T
RF RM
) is the total of the following terms:
+ T
OUT
Section 8-1
T
OUT
) when
RM
449