Omron CJ1W-DRM21 - Page 230

8 Communications Timing
8-12
CJ-series DeviceNet Units Operation Manual for NJ-series CPU Unit(W497)
• CPU Unit's processing time: T
CPU
x 6 + T
CPU
x 2 = T
CPU
x 8
The following time is required to process data with other clients before the CPU Unit starts
processing.
7 other clients/2 = Approximately cycle time x 3
If one processing requires two CPU Unit task periods, the time will be as follows:
CPU Unit task period x 3 x 2 = CPU Unit task period x 6
CPU Unit's processing time: T
CPU
x 2 = CPU Unit task period x 2
Total time will be as follows: CPU Unit task period x 8
• BYTE DATA READ response receiving time: T
BRR
DeviceNet header (3 bytes) + Number of words to be read x 2 = 203 bytes
Therefore, T
BRR
= 1 + 203 bytes/6 communications cycle time = 35 communications cycle
time
• DeviceNet Unit refresh time: T
RF
= 2 ms
The message response time will be as follows:
= T
RM
+ T
CPU
x 8 + T
RM
x 35 + T
RF
x 2 x 8 =3+80+105+32
= 220 ms
Precautions for Correct UsePrecautions for Correct Use
The above equations can be used to find the approximate message response time, but this is the
typical time, not the maximum time. The message response time will vary depending on the fre-
quency of message communications, the load on the remote node, the communications cycle
time, and other factors. For any one DeviceNet Unit, the message communications time can be
greatly increased due to heavy loads and the user program must be written to allow for this.