Siemens S7-1200 System Manual page 214

Basic instructions
7.2 Timer operations
Timer coil example
The -(TP)-, -(TON)-, -(TOF)-, and -(TONR)- timer coils must be the last instruction in a LAD
network. As shown in the timer example, a contact instruction in a subsequent network
evaluates the Q bit in a timer coil's IEC_Timer DB data. Likewise, you must address the
ELAPSED element in the IEC_timer DB data if you want to use the elapsed time value in
your program.
The pulse timer is started on a 0 to 1 transition of the Tag_Input bit value. The timer runs for
the time specified by Tag_Time time value.
As long as the timer runs, the state of DB1.MyIEC_Timer.Q=1 and the Tag_Output value=1.
When the Tag_Time value has elapsed, then DB1.MyIEC_Timer.Q=0 and the Tag_Output
value=0.
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 loaded with the assigned time-duration value..
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.
214
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG