Siemens SIMATIC S7-200 System Manual page 148

S7-200 Programmable Controller System Manual
Pulse Train Operation (PTO)
PTO provides a square wave (50% duty cycle) output for a specified number of pulses and a
specified cycle time. (See Figure 6-28.) PTO can produce either a single train of pulses or multiple
trains of pulses (using a pulse profile). You specify the number of pulses and the cycle time (in
either microsecond or millisecond increments):
Number of pulses:
-
Cycle time:
-
Specifying an odd number of microseconds or
milliseconds for the cycle time (such as 75 ms),
causes some distortion in the duty cycle causes some distortion in the duty cycle.
See Table 6-33 for pulse count and cycle time limitations.
Table 6-33 Pulse Count and Cycle Time in the PTO function
Pulse Count/Cycle TIme
Cycle time < 2 time units
Pulse count = 0
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.
Using the Position Control Wizard
The Position Control Wizard automatically handles single and multiple segment pipelining of PTO
pulses, pulse width modulation, SM Location configuration, and creating a profile table. The
information is here for your reference. It is recommended that you use the Position Control
Wizard. For more information about the Position Control Wizard, see Chapter 9.
Single-Segment Pipelining of PTO Pulses
In single-segment pipelining, you are responsible for updating the SM locations for the next pulse
train. After the initial PTO segment has been started, you must modify immediately the SM
locations as required for the second waveform and execute the PLS instruction again. The
attributes of the second pulse train are held in a pipeline until the first pulse train is completed.
Only one entry at a time can be stored in the pipeline. When the first pulse train completes, the
output of the second waveform begins, and the pipeline is made available for a new pulse train
specification. You can then repeat this process to set up the characteristics of the next pulse train.
Smooth transitions between pulse trains occur unless there is a change in the time base or the
active pulse train completes before a new pulse train setup is captured by the execution of the
PLS instruction.
134
1 to 4,294,967,295
10 µs to 65,535 µs or
2 ms to 65,535 ms.
Reaction
Cycle time defaults to 2 time units.
Pulse count defaults to 1 pulse.
Cycle Time
50% 50% 50%
Off On Off
Figure 6-28 Pulse Train Output (PTO)
50%
On