Analog Adjustments - Siemens Simatic S7-200 System Manual

Input/Output Control
8.5

Analog Adjustments

Your S7-200 CPU module provides one or two analog adjustments (potentiometers located
under the access cover of the module). You can adjust these potentiometers to increase or
decrease values that are stored in bytes of Special Memory (SMB28 and SMB29). 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.
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 guaranteed range of 10 to 200.
You 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.
Figure 8-6 shows an example program using the analog adjustment.
I0.0
SMB28
AC0
Q0.0
/
VW100
T33
Figure 8-6
8-8
LAD
Clear AC0.
MOV_W
EN
IN OUT
0 AC0
Read analog
MOV_B
adjustment 0.
EN
IN OUT
AC0
Save the word-based
MOV_W
value in VW100.
EN
IN OUT
VW100
T33
Use the word-based
TON
value as a preset for a
IN
timer. Turn on Q0.0
when T33 reaches
PT
preset.
Q0.0
Example of Analog Adjustment
STL
LD I0.0
MOVW 0, AC0
MOVB SMB28, AC0
MOVW AC0, VW100
LDN Q0.0
TON T33, VW100
LD T33
= Q0.0
S7-200 Programmable Controller System Manual
C79000-G7076-C230-02