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Message Communications Time Section 7-2
Program Example As shown in the preceding table, it takes time for DeviceNet communications
to start up. This programming uses flags in the Master Status Area to prevent
the Slaves’ I/O processing from being performed until remote I/O communica-
tions start up.
Note Refer to the Master Unit’s Operation Manual for details on the Master Status
Area 1.
This programming is for a CV-series PLC and a Master Unit with a unit num-
ber of 00.
7-2 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).
If the CPU Unit attempts to send another message or receives a message
from another node within the message communications time, the second
message or the message being received from another node may be
destroyed. Never execute a second communications instruction before the
message communications time has elapsed and never send messages to any
one node at intervals less than the message communications time.
Note 1. If send or receive messages are destroyed, error records will be placed in
the error history of the Master Unit. If an error occurs, read the error history
using the FINS command or monitor the error history from the Configura-
tor.
2. The following 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 communica-
tions cycle time, and other factors. For any one Master Unit, the message
communications time can be greatly increased due to heavy loads and the
user program must be written to allow for this.
The following equation can be used to compute the approximate message
communications time.
The Master only is
restarted.
The NS indicator flashes
red while the Master is
OFF.
8 seconds
The Slaves only are
restarted.
--- 10 seconds
Case Slave’s indicator status System startup time
Error/Communications
Stopped Flag
Remote I/O
Communications
Flag
Slaves' I/O pro-
cessing
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