Mitsubishi Electric MELSEC iQ-R-R6SFM - Page 345

21 DEVICES
21.3 User Device
343
21
Data configuration of long timer (LT/LST)
The long timer (LT) and the long retentive timer (LST) use four words (64 bits) for each point. If the most significant two words
are changed in a program, it is impossible to measure the time properly, because they are used by the system.
The current value of the long timer (LT) and the long retentive timer (LST) is 32-bit data. It can be specified by
the instructions which can specify signed or unsigned 32 bit data. (It cannot be specified with the BK +
Instruction.)
Precautions
This section describes the precautions when using the timer and long timer.
■Precautions about timer usage
• Do not describe more than one coil (the OUT T instruction) on the same timer during a single scanning. Doing so results
in improper measurement because the timer current value is updated when the coil for each timer is executed.
• When timer is not used for data collection for each scan: While the coil on a timer (e.g. T1) is turned on, the timer coil (the
OUT T instruction) cannot be skipped by the instructions such as the CJ. When the timer coil is skipped, proper
measurement is impossible because the timer current value is not updated. In addition, when the timer exists in a
subroutine program, be sure to execute a subroutine call including T1 coil only once for each scanning operation while the
coil of the timer (e.g. T1) is turned on. Otherwise proper measurement is impossible.
• The timer cannot be used in the initial execution type program, the fixed scan execution type program, or the event
execution type program where the occurrence of an interrupt is set to be a trigger. The timer can be used in standby type
programs if the coil of timer (OUT T instruction) is executed one time for one scan using a subroutine program.
• The timer cannot be used in interrupt programs. The timer can be used in subroutine programs or FB programs if the coil of
timer (OUT T instruction) is executed one time for one scan.
• When setting value is 0: The contact is turned on when the OUT T instruction is executed.
• Even when the setting value is increased after the timer time is up, the timer status does not change (time continues to be
up) and the timer does not operate.
• Do not set the timer setting value to 32768 or above. If used when set to 32768 or above, the timer contact may not turn on.
■Precautions about long timer usage
This section describes the precautions when using long timers (LT/LST).
• The long timer cannot be used in initial execution type programs.
• Even when the setting value is increased after the long timer time is up, the long timer status does not change (time
continues to be up) and the long timer does not operate.
LT0
+0
+1
+2
+3
+4
+5
+6
+7
LT1
1 word
(16 bits)
Current value of
LT0
(2 words)
Used in
system.
Current value of
LT0
(2 words)
Used in
system.