Section 3: The Memory Stack, LAST X, and Data Storage 33
Any number that is keyed in or results from the execution of a numeric
function is placed into the display (X-register). This action will cause
numbers already in the stack to lift, remain in the same register, or drop,
depending upon both the immediately preceding and the current
operation. Numbers in the stack are stored on a last-in, first-out basis.
The three stacks drawn below illustrate the three types of stack
movement. Assume x, y, z, and t represent any numbers which may be in
the stack.
Stack Lift No Stack Lift or Drop
T
t
z
T
t t
Z
z y
Z
z
z
Y
y x
Y
y y
X
x
π
X
x
x
|
$
¤
T
t
t
Z
z t
Y
y z
X
x x + y
Keys:
+
Notice the number in the T-register remains there when the stack drops,
allowing this number to be used repetitively as an arithmetic constant.
Stack Manipulation Functions
v. Pressing v separates two numbers keyed in one after the
other. It does so by lifting the stack and copying the number in the display
(X-register) into the Y-register. The next number entered then writes over
the value in the X-register; there is no stack lift. The example below shows
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