Siemens SIMATIC S7-200 System Manual page 85

Displaying the Status of the Program in Statement List
If you view your program using the STL editor, STEP 7-Micro/WIN 32 provides a
method of monitoring the execution status of the program on an
instruction-by-instruction basis. This status monitoring method is referred to as
STL status. The portion of your program for which STL status is enabled is called
the STL status window. This window is approximately the size of your
STEP 7-Micro/WIN 32 screen. Information obtained from the CPU is limited to 200
bytes or 25 lines. STL lines that appear on the screen that exceed these limits are
shown with "-" in the status window. Status information is gathered beginning from
the first STL statement at the top of the editor window. As you scroll down the
editor window, new information is gathered from the CPU. A typical STL Status
window is shown in Figure 4-19.
To open the STL status window, select the program status button from the toolbar
(Figure 4-19). Size the right margin of the STL program sheet to reveal the STL
status sheet.
When you turn STL status on, STL code appears on the left side of the STL Status
window; the status region containing operand values appears on the right. Indirect
address operands display both the value at the pointer address and the pointer
address. The pointer address is shown enclosed within parenthesis.
The STL Program Status button continuously updates values on the screen. If you
want to halt screen updates on the next data update, select the Triggered Pause
button (Figure 4-19). Current data will remain on the screen until you deselect the
button.
Operand values are shown in columns in the order in which they appear in each
instruction statement. These values are captured at the time each instruction is
executed and therefore reflect the actual execution status of the instruction.
The color of the status values indicates the execution status of the instruction:
Black indicates that the instruction executed correctly. Unconditional
instructions that are not included within an SCR block are always executed
regardless of the state of the logic stack. Conditional instructions use the logic
stack to determine execution.
Red indicates an error in execution. Refer to the page in Chapter 9 that
discusses the particular instruction for "Error Conditions that set ENO."
Gray indicates that the instruction did not execute because the top of stack
value (s0) = 0, or because the instruction is present within an SCR block that is
not enabled.
Blank indicates that the instruction has not executed.
Conditions that cause instructions not to be executed include:
Top of logic stack = 0.
The instruction was bypassed because of jumps or other constructs in your
program.
The PLC is not in RUN mode.
S7-200 Programmable Controller System Manual
A5E00066097-02
Basic Concepts for Programming an S7-200 CPU
4-35