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6-6
Message Communications Performance
Section 6-2
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6-2 Message Communications Performance
6-2-1 Message Communications Time
The message communications time is the time required from when the Master
Unit starts to send a message on the network until the entire message has
been sent when a message is being sent from one node to another. The mes-
sage will consist of data for a SEND or RECV instruction and a FINS com-
mand for an IOWR or CMND instruction.
Note If another message is sent before the message communications time elapses
or is a message is received from another node before the message communi-
cations time elapses, the response message being sent or the message being
received may be corrupted. When performing message communications it is
thus necessary to allow the message communications time to elapse before
performing message communications again using SEND, RECV, CMND, or
IOWR instructions and to allow the message communications time to elapse
between sending messages to the same node. If a send or receive message
is corrupted, a record will be stored in the error log in the Master Unit. Use a
FINS command to read the error record or use the Configurator to monitor the
error log.
The message communications time can be estimated using the following
equation:
Message communications time = Communications cycle time x {(number of
message bytes + 15)
÷
6 + 1}
The number of message bytes in the number of bytes after the FINS com-
mand code. The communications cycle time will depend on whether remote
I/O communications is being used and can be calculated as described next.
Only Message
Communications
(Remote I/O
Communications
Stopped)
Communications cycle time = 2 (see note) + 0.11 x TB + 0.6 ms
TB depends on the baud range as follows:
500 KB/s: 2, 250 KB/s: 4, 125 KB/s: 8
Note The communications cycle time when remote I/O communications are
stopped is 2 ms.
Slave I/O
processing
䋨 䋩
004
JMP #0001
䋨 䋩
005
JME #0001
2001
15 2001
14
I/O Data
Commuications
Flag
Error/Error
Communications
Stop Flag