Operation Of The Pulse Outputs - Siemens SIMATIC S7 System Manual

8.6.2

Operation of the pulse outputs

①
②
Since the PWM output can be varied from 0 to full scale, it provides a digital output that in
many ways is the same as an analog output. For example, the PWM output can be used to
control the speed of a motor from stop to full speed, or it can be used to control position of a
valve from closed to fully opened.
Two pulse generators are available for controlling high-speed pulse output functions: PWM
and Pulse train output (PTO). PTO is used by the motion control instructions. You can assign
each pulse generator to either PWM or PTO, but not both at the same time.
The two pulse generators are mapped to specific digital outputs as shown in the following
table. You can use onboard CPU outputs, or you can use the optional signal board outputs.
The output point numbers are shown in the following table (assuming the default output
configuration). If you have changed the output point numbering, then the output point
numbers will be those you assigned. Regardless, PTO1/PWM1 uses the first two digital
outputs, and PTO2/PWM2 uses the next two digital outputs, either on the CPU or on the
attached signal board. Note that PWM requires only one output, while PTO can optionally
use two outputs per channel. If an output is not required for a pulse function, it is available
for other uses.
NOTICE
Pulse-train outputs cannot be used by other instructions in the user program
When you configure the outputs of the CPU or signal board as pulse generators (for use
with the PWM or basic motion control instructions), the corresponding outputs addresses
(Q0.0, Q0.1, Q4.0, and Q4.1) are removed from the Q memory and cannot be used for
other purposes in your user program. If your user program writes a value to an output used
as a pulse generator, the CPU does not write that value to the physical output.
S7-1200 Programmable controller
System Manual, 11/2011, A5E02486680-05
Cycle time
Pulse width
Pulse width can be expressed as hundredths of the
cycle time (0 to 100), as thousandths (0 to 1000), as
ten thousandths (0 to 10000), or as S7 analog format.
The pulse width can vary from 0 (no pulse, always off)
to full scale (no pulse, always on).
101BExtended instructions
8.6 Pulse
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