Stack Pointer Configuration; Data To Be Saved To Stack Memory; Data To Be Reset From Stack Memory - NEC PD78081(A) User Manual

(3) Stack pointer (SP)
This is a 16-bit register to hold the start address of the memory stack area. Only the internal high-speed RAM
area (FE00H-FEFFH for the
PD78P083) can be set as the stack area.
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The SP is decremented ahead of write (save) to the stack memory and is incremented after read (reset) from
the stack memory.
Each stack operation saves/resets data as shown in Figures 3-10 and 3-11.
Caution Since RESET input makes SP contents indeterminate, be sure to initialize the SP before
instruction execution.
PUSH rp Instruction
SP _ 2
SP
SP _ 2
Register Pair Lower
SP _ 1
Register Pair Upper
SP
POP rp Instruction
SP Register Pair Lower
Register Pair Upper
SP + 1
SP SP + 2
CHAPTER 3 CPU ARCHITECTURE
PD78081, FD80H-FEFFH for the PD78082, and FD00H-FEFFH for the
Figure 3-9. Stack Pointer Configuration
Figure 3-10. Data to be Saved to Stack Memory
SP _ 2
SP
SP _ 2
SP _ 1
SP
Figure 3-11. Data to be Reset from Stack Memory
SP
SP + 1
SP SP + 2
SP
CALL, CALLF, and
CALLT Instruction
SP
PC7-PC0
PC15-PC8
RET Instruction
PC7-PC0
PC15-PC8
SP
0
Interrupt and
BRK Instruction
SP _ 3
SP _ 3
PC7-PC0
SP _ 2
PC15-PC8
SP _ 1
PSW
SP
RETI and RETB
Instruction
SP
PC7-PC0
SP + 1
PC15-PC8
SP + 2
PSW
SP + 3
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