Siemens SIMATIC STEP 7 V5.2 Getting Started page 67

Switching on the CPU and Checking the Operating Mode
Downloading individual blocks
In order to react to errors quickly in practice, blocks can be transferred individually to the
CPU using the drag and drop function.
When you download blocks, the operating mode switch on the CPU must be in either
"RUN-P" or "STOP" mode. Blocks downloaded in "RUN-P" mode are activated immediately.
You should therefore remember the following:
•
If error-free blocks are overwritten with faulty blocks, this will lead to a plant failure. You
can avoid this by testing your blocks before you download them.
•
If you do not observe the order in which blocks are to be downloaded – first the
subordinate blocks and then the higher-level blocks – the CPU will go into "STOP"
mode. You can avoid this by downloading the entire program to the CPU.
Programming online
In practice, you may need to change the blocks already downloaded to the CPU for test
purposes. To do this, double-click the required block in the online window to open the
LAD/STL/FBD program window. Then program the block as usual. Note that the
programmed block immediately becomes active in your CPU.
STEP 7 Getting Started
A5E00171228-01
Downloading and Debugging the Program
Turn the operating mode switch to
RUN-P. The green "RUN" LED lights
up and the red "STOP" LED goes out.
The CPU is ready for operation.
When the green LED lights up, you
can start testing the program.
If the red LED remains lit, an error has
occurred. You would then have to
evaluate the diagnostic buffer in order
to diagnose the error.
You can find more information under Help >
Contents and then under "Downloading and
Uploading" and under "Establishing an Online
Connection and Making CPU Settings".
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