Pto Operation - Siemens SIMATIC S7-200 System Manual

The PWM Update Method bit (SM67.4 or SM77.4) in the control byte is used to
specify the update type. Execute the PLS instruction to invoke the changes. Be
aware that if the time base is changed, an asynchronous update will occur
regardless of the state of the PWM Update Method bit.

PTO Operation

The PTO function provides for the generation of a square wave (50% duty cycle)
pulse train with a specified number of pulses. The cycle time can be specified in
either microsecond or millisecond increments. The cycle time has a range either
from 50 microseconds to 65,535 microseconds, or from 2 milliseconds to 65,535
milliseconds. If the specified cycle time is an odd number, some duty cycle
distortion will result. The pulse count has a range from 1 to 4,294,967,295 pulses.
If a cycle time of less than two time units is specified, the cycle time defaults to two
time units. If a pulse count of zero is specified, the pulse count defaults to one
pulse.
The PTO Idle bit in the status byte (SM66.7 or SM76.7) is provided to indicate the
completion of the programmed pulse train. In addition, an interrupt routine can be
invoked upon the completion of a pulse train (see Section 9.15 for information
about the interrupt and communication instructions). If you are using the multiple
segment operation, the interrupt routine will be invoked upon completion of the
profile table. See Multiple Segment Pipelining below.
The PTO function allows the chaining or pipelining of pulse trains. When the active
pulse train is complete, the output of a new pulse train begins immediately. This
allows continuity between subsequent output pulse trains.
This pipelining can be done in one of two ways: in single segment pipelining or in
multiple segment pipelining.
S7-200 Programmable Controller System Manual
A5E00066097-02
SIMATIC Instructions
9-51