Siemens SIMATIC S7 - Pulse Width Modulation (PWM)

Program instructions
7.7 Pulse output
S7-200 SMART
System Manual, V2.3, 07/2017, A5E03822230-AF
289
While the PTO profile is operating, the number of the currently active segment is available in
SMB166, SMB176, or SMB576.
Table 7- 16 Profile table format for multiple-segment PTO operation
1
Byte offset
Segment
Description of table entries
0
Number of segments: 1 to 255
2
1
#1
Starting Frequency (1 to 100,000 Hz)
5
Ending Frequency (1 to 100,000 Hz)
9 Pulse count (1 to 2,147,483,647)
13
#2
Starting Frequency (1 to 100,000 Hz)
17
Ending Frequency (1 to 100,000 Hz)
21
Pulse count (1 to 2,147,483,647)
(Continues)
#3
(Continues)
1
Entering
a profile offset and number of segments that places any part of the profile table outside of
V memory generates a non-fatal error. The PTO function does not generate a PTO output.
2
Entering a value of 0 for the number of segments generates a non-fatal error. No PTO output is
generated.
7.7.3
Pulse width modulation (PWM)
PWM provides three channels that allow a fixed cycle time output with a variable duty cycle.
Refer to the figure below. You can specify the cycle time and the pulse width in either
microsecond or millisecond increments:
•
Cycle time: 10 µs to 65,535 µs or 2 ms to
65,535 ms
•
Pulse width time: 0 µs to 65,535 µs or
0 ms to 65,535 ms
As shown in the following table, setting the pulse width equal to the cycle time (which makes
the duty cycle 100 percent) turns the output on continuously. Setting the pulse width to 0
(which makes the duty cycle 0 percent) turns the output off.
Note
When using a PWM with very short cycle times, you should take into account the switching
delay specifications for the output points and how the switching delay can affect the pulse
width time.
See Appendix A for the digital output switching delay for your CPU.