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Entry type: FAQ, Entry ID: 19623808, Entry date: 10/12/2004

Positioning Wizard for PTO/PWM in STEP 7 Micro/WIN V4.0

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What has changed in the Positioning Wizard for PTO/PWM in STEP 7 Micro/WIN V4.0?

The STEP 7 Micro/WIN V4.0 Positioning Wizard now also supports an improved pulse train function (linear inclinations, delayed interrupts, manual mode) for CPUs as from firmware version V2.0 in addition to the previous pulse trains (PTO) and the previous pulse train modulation (PWM). Nothing has changed in the Positioning Wizard for EM253 modules.

S7-200 CPUs with firmware V2.0 or higher have integrated linear change of pulse output as extension to the PTO function. CPUs with a firmware version lower than V2.0 do not support this function extension.

You can check the firmware of your CPU via the STEP 7 Micro/WIN menu command PLC > Information....

  • PTO:  
    The PTO always produces a square wave from a variable frequency. With the PTO function of the STEP 7 Micro/WIN Positioning Wizard you can configure more profiles for similar process steps of step motors (using the PTO function or the EM253 module). More detailed information on the PTO function of the Positioning Wizard is available in the STEP 7 Micro/WIN V4.0 Help.
  • PWM
    The PWM always produces a changeable pulse-duty factor from a constant frequency.

Differences between the "old" PTO (in CPUs with firmware versions lower than V2.0) and the new integrated PTO:

  • What are the differences between the "old" and "new" integrated PTO functions?
    Based on the change of cycle time in the "old" function, acceleration and delay were an exponential curve. With the new Positioning Wizard and a CPU of firmware version V2.0 and higher you obtain a linear change. Linear acceleration and delays are usually required for low-cost step motors.
  • Can an "old" program be used in a CPU with firmware >= V2.0 without having to change the program?
    It is possible to use the program for new CPUs too.
  • Can an "new" program also be used in a CPU with firmware < V2.0?
    No. The linear pulse output is not supported by the older CPUs.
  • How can I produce the "old" pulse output with the Positioning Wizard of STEP 7 Micro/WIN V4.0?
    You can produce the old pulse output just as before with the PLS statements.

Subprogram blocks that must be integrated into the user program are created by the Positioning Wizard for PTO and PWM.

Subprograms created by the Positioning Wizard for the integrated linear PTO on the CPU (as from firmware V2.0)

  • PTOx_ADV (jog): 
    Stops the actual continuous movement profile and increases the number of pulses specified in the profile defined by the Positioning Wizard. This subprogram is created when you have specified at least one continuous run at a fixed speed with the PTOx_ADV option enabled in the Positioning Wizard.
  • PTOx_CTRL (initialize and control PTO function):
    Must be activated in each cycle (at input EN) and may only be run once by a subprogram call in your program.
  • PTOx_RUN (run PTO profile): 
    Runs a specific positioning profile. This subprogram is generated by the Positioning Wizard for PTO configurations if one or more positioning profiles have been defined.
  • PTOx_MAN (PTO manual mode):
    Commands the program-controlled pulse generation.
  • PTOx_LDPOS (load position): 
    Loads a current position parameter into the PTO function. The PTO wizard creates this subprogram when a fast counter is chosen to count the pulses.

Subprogram created for PWM:

If you have selected the PWM mode in the STEP 7 Micro/WIN Wizard V4.0, the PWMxRUN subprogram is created.
In order to be able to implement PWM the time base for the time cycles must be defined in the Wizard.

  • Cycle:            cycle time: (2...65535 milliseconds/microseconds)
  • Pulse:            pulse duration: (2...65535 milliseconds/microseconds)

The subprogram created with STEP 7 Micro/WIN V4.0 is different from the subprogram created with STEP 7 Micro/WIN V3.2.x.

Fig. 1: STEP 7 Micro/WIN V3.2.x and V4.0 blocks

The block created by the Positioning Wizard is called "PWM_OUTx" with STEP 7 Micro/WIN V3.2.x and "PWM0_RUN" with STEP 7 Micro/WIN V4.0. A parameter (Error) for error identification has been added in the new block.

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