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Remote I/O Communications Characteristics Section 8-1
Note Although in the above diagram the Slaves are separated into two groups for
convenience, the actual physical positions in the Network are irrelevant.
Next, we can refer to 8-1-1 Communications Cycle Time and Refresh Time
and calculate the communications cycle time for each group as if they were
separate Networks.
In Networks with two Masters, the communications cycle time for the entire
Network will be the sum of the communications cycle times for the groups.
T
RM
= T
RM-A
+ T
RM-B
Although this example shows only two Masters in the Network, the total com-
munications cycle time for any Network can be calculated by dividing it into
groups and adding the communications cycle times of all groups.
8-1-4 System Startup Time
Master Function
This section describes the system startup time for a network operating with
the scan list enabled. The system startup time is the delay from the time that
the DeviceNet Unit (master) is turned ON until remote I/O communications
begin. Here, we assume that the scan list is enabled and that remote I/O com-
munications are set to start automatically at startup.
The following table shows the system startup times for two cases. In the first
case, the DeviceNet Unit starts up just after all of the Slaves’ power supplies
are turned ON. In the second case, the DeviceNet Unit is restarted while com-
munications are in progress.
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 prevents
the Slaves’ I/O processing from being performed until remote I/O communica-
tions start up.
Master A
Group A communications
cycle time: T
RM-A
Group A communications
cycle time: T
RM-B
Group A
Slave A
Slave B
Slave C
Group B
Master B
Slave D Slave E
Slave F
Case Slave’s indicator status System
startup time
The Master is
started just after
Slave startup.
The NS indicator is OFF or flashing green. 5 seconds
Just the Master is
restarted.
The NS indicator is flashes red while the Mas-
ter is OFF.
7 seconds
Just the Slaves are
restarted.
--- 9 seconds