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Message Communications Section 8-2
This programming is for a DeviceNet Unit with a unit number of 00.
Note Refer to 3-2 Allocated CIO Area Words for details on the Master Status Area.
Slave Function
It takes approximately four seconds from the time that the Devicenet Unit is
turned ON or restarted as a slave until remote I/O communications with the
master begin.
8-2 Message Communications
8-2-1 Message Communications Time
The message communications time is the time required from the time a Mas-
ter Unit starts to send a message over the Network to another node until the
Master Unit completes sending the message (data for SEND(192)/
RECV(193) and FINS commands for CMND(194)/IOWR).
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 FINS command code
The communications cycle time depends on whether or not remote I/O com-
munications 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
B
+ 0.6 [ms]
T
B
: The baud rate factor
(500 kbps: T
B
= 2; 250 kbps: T
B
= 4; 125 kbps: T
B
= 8)
Note The communications cycle time will be 2 ms even if remote I/O communica-
tions are not being used.
Remote I/O and Message Communications
Performing message communications in addition to remote I/O communica-
tions will increase the message communications time.
Communications cycle time=
Communications cycle time for remote I/O communications only
+ 0.11 × T
B
+ 0.6 [ms]
T
B
: The baud rate factor
(500 kbps: T
B
= 2; 250 kbps: T
B
= 4; 125 kbps: T
B
= 8)
(Varies depending on the baud rate.)
Unit Error
(n+10, bit 00)
Remote I/O
Communications
(n+12, bit 15)
Slaves' I/O
processing
1512
15
1510
00