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8 Communications Timing
8-2
Message Communications
8-2-1
Message Communications Time
The message communications time is the time required from the time a Master Unit starts to send a
message over the Network to another node until the Master Unit completes sending the message.
The following equation can be used to compute the approximate message communications time.
Message communications time =
Communications cycle time x ((No. of message bytes + 15) ÷ 6 + 1)
No. of message bytes: No. of data bytes following the command code (16#2801)
The communications cycle time depends on whether or not remote I/O communications are being used.
Message Communications Only (No Remote I/O Communications)
The following equation can be used to compute the message communications time when remote I/O
communications are not being used.
Communications cycle time =
2 (see note) + 0.11 × T
T
:
The baud rate factor
B
(500 kbit/s: T
Note The communications cycle time will be 2 ms even if remote I/O communications are not being
used.
Remote I/O and Message Communications
Performing message communications in addition to remote I/O communications will increase the
message communications time.
Communications cycle time=
Communications cycle time for remote I/O communications only
+ 0.11 × T
T
:
The baud rate factor
B
(500 kbit/s: T
(Varies depending on the baud rate.)
Precautions for Correct Use
Precautions for Correct Use
The above equations can be used to find the approximate message communications time, but
this is a typical time, not the maximum time. The message communications time will vary
depending on the frequency of message communications, the load on the remote node, the
communications cycle time, and other factors. For any one Master Unit, the message communi-
cations time can be greatly increased due to heavy loads and the user program must be written
to allow for this.
8-10
+ 0.6 [ms]
B
= 2; 250 kbit/s: T
= 4; 125 kbit/s: T
B
B
+ 0.6 [ms]
B
= 2; 250 kbit/s: T
= 4; 125 kbit/s: T
B
B
CJ-series DeviceNet Units Operation Manual for NJ-series CPU Unit(W497)
= 8)
B
= 8)
B
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