Calculator User Manual

Pop Top of Stack to Low Accumulator POP
7-135 Assembly Language Instructions
Syntax POP
Operands None
Opcode
0123456789101112131415
0100110001111101
Execution Increment PC, then ...
(TOS) → ACC(15:0)
0 → ACC(31:16)
Pop stack one level
Status Bits None
Description The content of the top of the stack (TOS) is copied to the low accumulator, and
then the stack values move up one level. The upper half of the accumulator
is set to all zeros.
The hardware stack functions as a last-in, first-out stack with eight locations.
Any time a pop occurs, every stack value is copied to the next higher stack lo-
cation, and the top value is removed from the stack. After a pop, the bottom
two stack words will have the same value. Because each stack value is copied,
if more than seven stack pops (using the POP, POPD, RETC, or RET instruc-
tions) occur before any pushes occur, all levels of the stack will contain the
same value. No provision exists to check stack underflow.
Words 1
Cycles for a Single POP Instruction
ROM
DARAM SARAM External
1 1 1 1+p
Cycles for a Repeat (RPT) Execution of a POP Instruction
ROM
DARAM SARAM External
n n n n+p
Cycles