User Manual

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11.16 Downloading in RUN mode
Easy Book
272 Manual, 03/2014, A5E02486774-AF
11.16
Downloading in RUN mode
The CPU supports "Download in RUN mode". This capability is intended to allow you to
make small changes to a user program with minimal disturbance to the process being
controlled by the program. However, implementing this capability also allows massive
program changes that could be disruptive or even dangerous.
WARNING
Risks with downloading in RUN mode
When you download changes to the CPU in RUN mode, the changes immediately affect
process operation. Changing the program in RUN mode can result in unexpected system
operation, which could cause death or serious injury to personnel, and/or damage to
equipment.
Only authorized personnel who understand the effects of RUN mode changes on system
operation should perform a download in RUN mode.
The "Download in RUN mode" feature allows you to make changes to a program and
download them to your CPU without switching to STOP mode:
● You can make minor changes to your current process without having to shut down (for
example, change a parameter value).
● You can debug a program more quickly with this feature (for example, invert the logic for
a normally open or normally closed switch).
You can make the following program block and tag changes and download them in RUN
mode:
● Create, overwrite, and delete Functions (FC), Function Blocks (FB), and Tag tables.
● Create, delete, and overwrite Data Blocks (DB) and instance data blocks for Function
Blocks (FB). You can add to DB structures and download them in RUN mode. The CPU
can maintain the values of existing block tags and initialize the new data block tags to
their initial values, or the CPU can set all data block tags to initial values, depending on
your configuration settings. You cannot download a web server DB (control or fragment)
in RUN mode.
● Overwrite Organization Blocks (OB); however, you cannot create or delete OBs.
You can download a maximum number of twenty blocks in RUN mode at one time. If you
must download more than twenty blocks, you must place the CPU in STOP mode.
If you download changes to a real process (as opposed to a simulated process, which you
might do in the course of debugging a program), it is vital to think through the possible safety
consequences to machines and machine operators before you download.
Note
If the CPU is in RUN mode and program changes have been made, STEP 7 always tries to
download in RUN first. If you do not want this to happen, you must put the CPU into STOP.
If the changes m
ade are not supported in "Download in RUN", STEP 7 prompts the user that
the CPU must go to STOP.