Siemens SIMATIC S7 System Manual page 175
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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.
Configuring a pulse channel for PWM
To prepare for PWM operation, first configure a pulse channel in the device configuration by
selecting the CPU, then Pulse Generator (PTO/PWM), and choose either PWM1 or PWM2.
Enable the pulse generator (check box). If a pulse generator is enabled, a unique default
name is assigned to this particular pulse generator. You can change this name by editing it
in the "Name:" edit box, but it must be a unique name. Names of enabled pulse generators
will become tags in the "constant" tag table, and will be available for use as the PWM
parameter of the CTRL_PWM instruction.
NOTICE
The maximum pulse frequency of the pulse output generators is 100 KHz for the digital
outputs of the CPU and 20 KHz for the digital outputs of the signal board. However, STEP 7
Basic does not alert you when you configure an axis that with a maximum speed or
frequency that exceeds this hardware limitation. This could cause problems with your
application, so always ensure that you do not exceed the maximum pulse frequency of the
hardware.
You have the option to rename the pulse generator, add a comment, and assign parameters
as follows:
● Pulse generator used as follows: PWM or PTO (choose PWM)
● Output source: onboard CPU or Signal Board
● Time base: milliseconds or microseconds
S7-1200 Programmable controller
System Manual, 11/2009, A5E02486680-02
Description
PTO 1
Onboard CPU
Signal board
PWM 1
Onboard CPU
Signal board
PTO 2
Onboard CPU
Signal board
PWM 2
Onboard CPU
Signal board
Default output assignment
Pulse
Q0.0
Q4.0
Q0.0
Q4.0
Q0.2
Q4.2
Q0.2
Q4.2
Programming instructions
6.2 Extended instructions
Direction
Q0.1
Q4.1
--
--
Q0.3
Q4.3
--
--
175
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