Siemens SIMATIC S7 System Manual page 173

Reset timer -(RT)- and Preset timer -(PT)- coils
These coil instructions can be used with box or coil timers and can be placed in a mid-line
position. The coil output power flow status is always the same as the coil input status. When
the -(RT)- coil is activated, the ELAPSED time element of the specified IEC_Timer DB data
is reset to 0. When the -(PT)- coil is activated, the PRESET time element of the specified
IEC_Timer DB data is reset to 0.
Note
When you place timer instructions in an FB, you can select the "Multi-instance data block"
option. The timer structure names can be different with separate data structures, but the
timer data is contained in a single data block and does not require a separate data block for
each timer. This reduces the processing time and data storage necessary for handling the
timers. There is no interaction between the timer data structures in the shared multi-instance
DB.
Operation of the timers
Table 7- 21 Types of IEC timers
Timer
TP: Pulse timer
The TP timer generates a pulse with a preset width
time.
TON: ON-delay timer
The TON timer sets output Q to ON after a preset time
delay.
S7-1200 Programmable controller
System Manual, 11/2011, A5E02486680-05
Timing diagram
100BBasic instructions
7.2 Timers
173