Siemens SIMATIC S7 System Manual page 286

Program instructions
7.7 Pulse output
The PTO/PWM generators and the process image register share the use of Q0.0, Q0.1, and
Q0.3. When a PTO or PWM function is active on Q0.0, Q0.1, or Q0.3, the PTO/PWM
generator has control of the output, and normal use of the output point is inhibited. The
output waveform is not affected by the state of the process image register, the forced value
of the point, or the execution of immediate output instructions. When the PTO/PWM
generator is inactive, control of the output reverts to the process image register. The process
image register determines the initial and final state of the output waveform, causing the
waveform to start and end at a high or low level.
Note
PTO/PWM through the PLS instruction is not possible if the selected output point is already
configured for use with motion control through use of the Motion wizard.
The PTO/PWM outputs must have a minimum load of at least 10% of rated load to provide
crisp transitions from off to on, and from on to off.
Before enabling PTO/PWM operation, set the value of the process image register for Q0.0,
Q0.1, and Q0.3 to 0.
Default values for all control bits, cycle time/frequency, pulse width, and pulse count values
are 0.
Note
The Pulse Output (PLS) instruction can only be used with the following S7-200 SMART
CPUs:
• SR20 / ST20 (Two channels, Q0.0 and Q0.1)
• SR30 / ST30, SR40 / ST40, and SR60 / ST60 (Three channels, Q0.0, Q0.1, and Q0.3)
286
System Manual, V2.3, 07/2017, A5E03822230-AF
S7-200 SMART