Allen-Bradley 1779-KFMR User Manual page 128

Chapter 8
access to the PLC-2 memory during a download if your download
procedure follows this order:
Enter Download Mode
Set Data Table Size (if Required)
Physical Write
.
.
.
Physical Write
Physical Read (Verification)
Exit Download/Upload Mode
If you download a program that requires a change in data table size, send
a set data table size command before sending physical write commands
containing the new program. If you send a set data table size command
that increases the size of the data table, send a physical write command to
clear out that part of the data table that had previously been in the
program area.
Whenever you download a program, always write zeros into the unused
portion of memory following the program.
After you write the new program into the PLC-2 memory, verify the new
program through physical read commands before exiting the download
mode. However, you will be unable to verify the first word in the
program until after exiting the download mode. The 1779-KP2 interface
does not write that word into memory until exiting the download mode.
While in the download mode, the interface writes an end (of program)
instruction into the first word of the program. This end instruction keeps
the PLC-2 processor from executing the program until the download
mode is exited. If the download cannot be completed, the end instruction
remains as the first word of the program.
For the enter download mode command to be accepted by an interface for
a PLC-2/15 or PLC-2/30 processor, the mode-select switch must be in the
RUN/PROG or PROG position. The mode-select switch of a PLC-2/20 or
Mini-PLC-2 processor can be in any position; however, we recommend
that you select the PROG position. Results of the enter download mode
command are: