Samsung KS57C2308 Manual page 22

ADDRESS SPACES
POP OPERATIONS
For each push operation there is a corresponding pop operation to write data from the stack back to the source
register or registers: for the PUSH instruction it is the POP instruction; for CALL, the instruction RET or SRET; for
interrupts, the instruction IRET. When a pop operation occurs, the SP is incremented by a number determined by
the type of operation and points to the next free stack location.
POP Instructions
A POP instruction references the SP to write data stored in two 4-bit stack locations back to the register pairs and
SB register. The value of the lower 4-bit register is popped first, followed by the value of the upper 4-bit register.
After the POP has executed, the SP is incremented by two and points to the next free stack location.
RET and SRET Instructions
The end of a subroutine call is signaled by the return instruction, RET or SRET. The RET or SRET uses the SP
to reference the six 4-bit stack locations used for the CALL and to write this data back to the PC, the EMB, and
the ERB. After the RET or SRET has executed, the SP is incremented by six and points to the next free stack
location.
IRET Instructions
The end of an interrupt sequence is signaled by the instruction IRET. IRET references the SP to locate the six
4-bit stack addresses used for the interrupt and to write this data back to the PC and the PSW. After the IRET
has executed, the SP is incremented by six and points to the next free stack location.
SP
SP
SP + 1
SP + 2
NOTE: PC13 is used for KS57C2316/P2316 microcontroller
2-14
POP
SP + 2)
SP
LOWER
SP + 1
UPPER
SP + 2
SP + 3
SP + 4
SP + 5
SP + 6
Figure 2-8. Pop-Type Stack Operations
RET OR SRET
SP SP + 6)
PC11 – PC8
0 0 PC13 PC12
PC3 – PC0
PC7 – PC4
0 0 EMB ERB
PSW
0 0 0 0
KS57C2308/P2308/C2316/P2316
IRET
SP SP + 6)
SP
PC11 – PC8
SP + 1
0 0 PC13 PC12
SP + 2
PC3 – PC0
SP + 3
PC7 – PC4
SP + 4
IS1 IS0 EMB ERB
PSW
SP + 5
C SC2 SC1 SC0
SP + 6