Siemens Simatic S7-200 System Manual page 127

Displaying the Status of the Program in Ladder Logic
As shown in Figure 6-13, the program editor of STEP 7-Micro/WIN allows you to monitor the
status of the online program. (The program must be displaying ladder logic.) This allows you
to monitor the status of the instructions in the program as they are executed by the CPU.
Contacts
Network 1
"Start_1"
"Pump_1"
Figure 6-13
Using a Status Chart to Force Specific Values
The S7-200 CPU allows you to force any or all of the I/O points (I and Q bits) and variables to
specific values. In addition, you can also force up to 16 internal memory values (V or M) or
analog I/O values (AI or AQ). V memory or M memory values can be forced in bytes, words,
or double words. Analog values are forced as words only, on even-byte boundaries (such as
AIW6 or AQW14). All forced values are stored in the permanent EEPROM memory of the
CPU.
Because the forced data might be changed during the scan cycle (either by the program, by
the I/O update cycle, or by the communications-processing cycle), the CPU reapplies the
forced values at various times in the scan cycle. Figure 6-14 shows the scan cycle,
highlighting when the CPU updates the forced variables.
The Force function overrides an immediate-read or immediate-write instruction. The Force
function also overrides an output that was configured to go to a specified value on transition
to STOP mode: if the CPU goes to STOP mode, the output reflects the forced value and not
the configured value.
S7-200 Programmable Controller System Manual
C79000-G7076-C230-02
Basic Concepts for Programming an S7-200 CPU
Normally Open
F2
Fill the tank with Paint Ingredient 1 and monitor the tank.
"Stop_1" "High_Level"
Displaying the Status of a Program in Ladder Logic
F3
F4
F5 F6 F7 F8
"Pump_1"
F10
6-17