INSTRUCTION SET
S3C80A5B
6-64
POPUD
—
Pop User Stack (Decrementing)
POPUD
dst,src
Operation:
dst
←
src
IR
←
IR – 1
This instruction is used for user-defined stacks in the register file. The contents of the register file
location addressed by the user stack pointer are loaded into the destination. The user stack pointer
is then decremented.
Flags:
No flags are affected.
Format:
Bytes
Cycles
Opcode
(Hex)
Addr Mode
dst src
opc
src
dst
3
8
92
R
IR
Example:
Given: Register 00H = 42H (user stack pointer register), register 42H = 6FH, and
register 02H = 70H:
POPUD
02H,@00H
→
Register 00H = 41H, register 02H = 6FH, register 42H = 6FH
If general register 00H contains the value 42H and register 42H the value 6FH, the statement
"POPUD 02H,@00H" loads the contents of register 42H into the destination register 02H. The user
stack pointer is then decremented by one, leaving the value 41H.