Precautions - Mitsubishi Electric MELSEC iQ-R-R00CPU User Manual

Precautions

The following lists the precautions for using a program executed in both systems.
Item
Program execution time
Constant scan
Time required for system switching
Program Execution type change
execution type
Initial execution type
Interrupt disabled or enabled state
Tracking transfer
Device Timer (T)
Long timer (LT) and long
retentive timer (LST)
Interrupt pointer (I)
Restricted instructions
Standard TIMER__M
function block
TP(_E), TON(_E),
TOF(_E)
Ethernet Socket communications
Communications using
the fixed buffer
Program execution time
Set a program execution time of the standby system to be shorter than that of the control system. When a program execution
time of the standby system is longer than the total program execution time of the control system, the control system starts the
next scan before the standby system has received tracking data, causing a continuation error. If the systems are switched in
this state, the latest data may not be reflected on the new control system.
When a program execution time of the standby system cannot be shortened, set SD1662 (Tracking transfer data receive
completion wait time) to extend a waiting time for tracking data receive completion of the control system. With this setting, the
control system CPU module starts the next scan after the standby system has received tracking data. Even if the systems are
switched, the control can be continued based on the latest data.
37 FUNCTIONS
650
37.5 Program Execution in Both Systems
Description
Set a program execution time of the standby system to be shorter than that of the
control system.
The constant scan function is invalid for the standby system.
If system switching is attempted to be performed while a program executed in both
systems is being executed, the system is switched after the END instruction is
completed. Thus, a time required for system switching may be extended.
The execution type of a program executed in both systems is not taken over at
system switching.
Even if the systems are switched after the execution type is changed by using a
program control instruction (PSCAN(P), PSTOP(P), or POFF(P) instruction) on the
old control system, the program is executed on the new control system with the
execution type of the old standby system.
When the systems are switched while an initial execution type program set as a both
systems execution program is being executed, the initial execution type program is
executed twice on the new control system CPU module.
The old standby system is switched to the new control system after the initial
execution type program has been completed, and then the initial execution type
program is executed again.
The control system and standby system have individual interrupt disabled or enabled
state because the states are not transferred.
Do not set global devices used in a program executed in both systems as a tracking
transfer target. When using labels in a program executed in both systems, use local
labels. When using FBs in a program executed in both systems, use local FBs.
When the control system is switched to the standby system, the current value of the
timer is not updated in the first scan of the new standby system and a timeout does
not occur. As a result, an error of the time required for system switching + one scan is
produced at system switching.
When the long timer (LT) or long retentive timer (LST) is used in the standby system,
time is not measured and a timeout does not occur.
After the standby system has been switched to the control system, the long timer (LT)
or long retentive timer (LST) is started up. To measure time in the standby system,
use the timer (T).
The interrupt pointer (I) cannot be used for the standby system.
Some instructions have restrictions when they are used in a program executed in
both systems.
When the control system is switched to the standby system, the current value of the
timer is not updated in the first scan of the new standby system and a timeout does
not occur. As a result, an error of the time required for system switching + one scan is
produced at system switching.
When these function blocks are used in the standby system, time is not measured
and a timeout does not occur.
After the standby system has been switched to the control system, TP(_E), TON(_E),
or TOF(_E) is started up.
When data is sent to the Ethernet-equipped module of the standby system, the data
receive processing is not performed because the Ethernet-equipped module discards
the received data.
Reference
Page 650 Program
execution time
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Page 651 Tracking
transfer
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Page 651 Restricted
instructions
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 MELSEC iQ-R
Ethernet User's Manual
(Application)