手册第8章
Hardware Troubleshooting Guide andSoftware Debugging Tools
Forcing Specific Values
The S7-200 allows you to force any or all of the I/O points (I and Q bits). In addition, you can also force up to 16 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-numbered byte boundaries, such as AIW6 or AQW14. All forced values are stored in the permanent EEPROM
memory of the S7-200.
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 S7-200 reapplies the forced values at various times in the scan cycle.
- Reading the inputs: The S7-200 applies the forced values to the inputs as they are read.
- Executing the control logic in the program: The S7-200 applies the forced values to all immediate
I/O accesses. Forced values are applied for up to 16 memory values after the program has been executed.
- Processing any communications requests: The S7-200 applies the forced values to all read/write communications accesses.
- Writing to the outputs: The S7-200 applies the forced values to the outputs as they are written.
You can use the Status Chart to force values. To force a new value, enter the value in the New Value column of the Status Chart, then press the Force button on the toolbar.
To force an existing value, highlight the value in the Current Value column then press the Force button Execute the Program Process any Communications Requests Perform the CPU Diagnostics Writes to the outputs Reads the inputs Scan Cycle column, button.