287
Index Registers Section 6-2
Note Actually, the first two words of the stack contain the PLC memory address of
the last word in the stack and the next word contains the stack pointer.
FIFO (First-in First-out) Processing
The following diagram shows the operation of a first-in first-out (FIFO) stack.
LIFO (Last-in First-out) Processing
The following diagram shows the operation of a last-in first-out (LIFO) stack.
Manipulating Specific Table Data
Individual entries in a table can be read, writing, inserted, or deleted. The fol-
lowing diagram shows an example for reading.
B
A
B
A
A
C
A
C
B
Pointer address Pointer address
Pointer address
Pointer address
Stack
region
(The above diagram shows
the status of the pointer
data before data is added.)
A
A
B
X
C
Pointer address
Reads the oldest word of data stored in
the stack. Each time that a word is read,
the pointer is decremented by one to
indicate the next address for storage.
A
B
X
X
V
W
1
Pointer address
Reads most recent word of data stored
in the stack. Each time that a word is
read, the pointer is decremented by one
to indicate the next address for storage.
Data at the position that was read
remains unchanged.
A
V
B
W
X
V
−n
Pointer address
Read
Data is read from a specific offset from
the point address in the table.
Manipulating specific table data can be
used, for example, in tracing items on a
conveyor.
An offset from the point
address is specified.
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