Pulse Output Instruction - Siemens SIMATIC S7-200 System Manual

Pulse Output Instruction

The Pulse Output instruction (PLS) is used to control the
Pulse Train Output (PTO) and Pulse Width Modulation
(PWM) functions available on the high-speed outputs (Q0.0
and Q0.1).
Position The improved Position Control Wizard creates instructions
Control
customized to your application that simplify your
programming tasks and take advantage of the extra
features of the S7-200 CPUs. Refer to Chapter 9 for more
information about the Position Control Wizard.
You can continue to use the old PLS instruction to create
your own motion application, but the linear ramp on the PTO
is only supported by instructions created by the improved
Position Control Wizard.
PTO provides a square wave (50% duty cycle) output with
user control of the cycle time and the number of pulses.
PWM provides a continuous, variable duty cycle output with user control of the cycle time and the
pulse width.
The S7-200 has two PTO/PWM generators that create either a high-speed pulse train or a pulse
width modulated waveform. One generator is assigned to digital output point Q0.0, and the other
generator is assigned to digital output point Q0.1. A designated special memory (SM) location
stores the following data for each generator: a control byte (8-bit value), a pulse count value (an
unsigned 32-bit value), and a cycle time and pulse width value (an unsigned 16-bit value).
The PTO/PWM generators and the process-image register share the use of Q0.0 and Q0.1. When
a PTO or PWM function is active on Q0.0 or Q0.1, 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.
Table 6-32 Valid Operands for Pulse Output Instruction
Inputs/Outputs
Q0.X
Tip
Before enabling PTO or PWM operation, set the value of the process-image register for Q0.0
and Q0.1 to 0.
Default values for all control bits, cycle time, pulse width, and pulse count values are 0.
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.
Refer to the Programming Tips on the documentation CD for programs that use the PLS
instruction for PTO/PWM operation. See Tip 7, Tip 22, Tip 23, Tip 30, and Tip 50.
Programming
Tips
Data Types Operands
WORD Constant:
S7-200 Instruction Set
0 (= Q0.0) or 1 (= Q0.1)
Chapter 6
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