Specifications

SIMATIC Instructions
9-17
S7-200 Programmable Controller System Manual
C79000-G7076-C233-01
Understanding the S7-200 Timer Instructions
You can use timers to implement time-based counting functions. The S7-200
instruction set provides three types of timers as shown below. Table 9-2 shows the
actions of the different timers.
 On-Delay Timer (TON) for timing a single interval
 Retentive On-Delay Timer (TONR) for accumulating a number of timed intervals
 Off-Delay Timer (TOF) for extending time past a false condition (in other words,
such as cooling a motor after it is turned off)
Table 9-2 Timer Actions
Timer
Type
Current >= Preset
Enabling Input
ON
Enabling Input
OFF
Power Cycle/
First Scan
TON Timer bit ON,
Current continues
counting to 32,767
Current value
counts time
Timer bit OFF,
Current value = 0
Timer bit OFF,
Current value = 0
TONR Timer bit ON,
Current continues
counting to 32,767
Current value
counts time
Timer bit and
current value
maintain last state
Timer bit OFF,
Current value may
be maintained
1
TOF Timer bit OFF,
Current = Preset,
stops counting
Timer bit ON,
Current value = 0
Timer counts after
ON to OFF
transition
Timer bit OFF,
Current value = 0
1
The retentive timer current value can be selected for retention through a power cycle. See Section 5.3 for information
about memory retention for the S7-200 CPU.
Note
The Reset (R) instruction can be used to reset any timer. The TONR timer can
only be reset by the Reset instruction. The Reset instruction performs the following
operations:
Timer Bit = OFF
Timer Current = 0
After a reset, TOF timers require the enabling input to make the transition from ON
to OFF in order to restart.