Siemens SIMATIC S7-200 System Manual page 64

S7-200 Programmable Controller System Manual
The S7-200 Provides Analog Adjustment Potentiometers
The analog adjustment potentiometers are located under the front access cover of the module.
You can adjust these potentiometers to increase or decrease values that are stored in bytes of
Special Memory (SMB). These read-only values can be used by the program for a variety of
functions, such as updating the current value for a timer or a counter, entering or changing the
preset values, or setting limits. Use a small screwdriver to make the adjustments: turn the
potentiometer clockwise (to the right) to increase the value, and counterclockwise (to the left) to
decrease the value.
SMB28 holds the digital value that represents the position of analog adjustment 0. SMB29 holds
the digital value that represents the position of analog adjustment 1. The analog adjustment has a
nominal range of 0 to 255 and a repeatability of ±2 counts.
Sample Program for Referencing the Value Entered with the Analog Adjustment Potentiometers
The S7-200 Provides High-speed I/O
High-Speed Counters
The S7-200 provides integrated high-speed counter functions that count high speed external
events without degrading the performance of the S7-200. See Appendix A for the rates supported
by your CPU model. Each counter has dedicated inputs for clocks, direction control, reset, and
start, where these functions are supported. You can select different quadrature modes for varying
the counting rate. For more information on high-speed counters, see Chapter 6.
High-Speed Pulse Output
The S7-200 supports high-speed pulse outputs, with outputs Q0.0 and Q0.1 generating either a
high-speed pulse train output (PTO) or pulse width modulation (PWM).
The PTO function provides a square wave (50% duty cycle) output for a specified number of
pulses (from 1 to 4,294,967,295 pulses) and a specified cycle time (in either microsecond or
millisecond increments. You can program the PTO function to produce either one train of pulses or
a pulse profile consisting of multiple trains of pulses. For example, you can use a pulse profile to
control a stepper motor through a simple ramp up, run, and ramp down sequence or more
complicated sequences.
The PWM function provides a fixed cycle time with a variable duty cycle output, with the cycle time
and the pulse width specified in either microsecond or millisecond increments. When the pulse
width is equal to the cycle time, the duty cycle is 100 percent and the output is turned on
continuously. When the pulse width is zero, the duty cycle is 0 percent and the output is turned off.
For more information on the high-speed pulse output instruction, see Chapter 6. For more
information about using PTO in open loop motion control, see Chapter 9.
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Network 1 //Read analog adjustment 0 (SMB28).
//Save the value as an integer in VW100.
LD I0.0
BTI SMB28, VW100
Network 2 //Use the integer value (VW100) as
//a preset for a timer.
LDN Q0.0
TON T33, VW100
Network 3 //Turn on Q0.0 when T33 reaches
//the preset value.
LD T33
= Q0.0