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4-6-3 Clearing Memory
Using the Memory Clear operation it is possible to clear all or part of the UM area
(RAM or EEPROM), and the IR, HR, AR, DM, EM and TC areas. Unless other-
wise specified, the clear operation will clear all of the above memory areas. The
UM area will not be cleared if the write-protect switch (pin 1 of the CPU Unit’s DIP
switch) is set to ON.
Before beginning to programming for the first time or when installing a new pro-
gram, all areas should normally be cleared. Before clearing memory, check to
see if a program is already loaded that you need. If you need the program, clear
only the memory areas that you do not need, and be sure to check the existing
program with the program check key sequence before using it. The check se-
quence is provided later in this section. Further debugging methods are pro-
vided in Section 7 Program Monitoring and Execution. To clear all memory areas
press CLR until all zeros are displayed, and then input the keystrokes given in
the top line of the following key sequence. The branch lines shown in the se-
quence are used only when performing a partial memory clear, which is de-
scribed below.
Memory can be cleared in PROGRAM mode only. The following table shows
which memory areas will be cleared for the 3 memory clearing operations (all
clear, partial clear, memory clear).
Memory Area All clear Partial clear Memory clear
I/O words Cleared Cleared Cleared
Work words Cleared --- Cleared
HR, AR, TC, DM, fixed DM Cleared Cleared Cleared
Expansion DM Cleared --- Cleared
EM Cleared Cleared Cleared
I/O comments Cleared --- ---
Ladder program Cleared Cleared Cleared
UM Allocation information Cleared --- ---
Note 1. The error history area (DM 6000 to DM 6030) will not be cleared when the
DM area is cleared.
2. When the PC Setup area (DM 6600 to DM 6655 in fixed DM) is cleared, the
settings will be returned to their factory-set defaults.
3. When the All Clear operation is executed, the ladder program area will be
allocated entirely to the ladder program. (The expansion DM and I/O com-
ment areas will be set to 0 KW.) Also , all EM banks will be cleared.
All Clear The key sequence for all clear is shown below.
Preparation for Operation Section 4-6