Siemens SIMATIC S7-200 - Understanding the S7-200 Timer Instructions; Timer Actions

SIMATIC Instructions
9-17
S7-200 Programmable Controller System Manual
A5E00066097-02
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, 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 Reset instruction
performs the following operations:
Timer Bit = OFF
Timer Current = 0
The TONR timer can only be reset by the Reset instruction.
After a reset, TOF timers require the enabling input to make the transition from ON
to OFF in order to restart.