Operation Of The Pulse Outputs - Siemens S7-1200 System Manual

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Because the CPU processes the request when the CTRL_PWM instruction is executed,

parameter BUSY will always report FALSE. If an error is detected, then ENO is set to

FALSE, and parameter STATUS contains a condition code.

The pulse width will be set to the initial value configured in device configuration when the

CPU first enters RUN mode. You write values to the Q-word location specified in device

configuration ("Output addresses" / "Start address:") as needed to change the pulse width.

You use an instruction such as a move, convert, math, or PID box to write the desired pulse

width to the appropriate Q word. You must use the valid range for the Q-word value (percent,

thousandths, ten-thousandths, or S7 analog format).

Digital I/O points assigned to PWM and PTO cannot be forced

The digital I/O points used by the pulse-width modulation (PWM) and pulse-train output

(PTO) devices are assigned during device configuration. When digital I/O point addresses

are assigned to these devices, the values of the assigned I/O point addresses cannot be

modified by the Watch table force function.

Table 8- 148 Value of the STATUS parameter

Operation of the pulse outputs

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.

Four 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.

S7-1200 Programmable controller

System Manual, 03/2014, A5E02486680-AG

PWM identifier does not address a valid PWM.

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).

Extended instructions