NEC uPD78P078 - Manual (Page 112)

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CHAPTER 5 CPU ARCHITECTURE
SP
15 0
SP15 SP14 SP13 SP12 SP11 SP10 SP9 SP8 SP7 SP6 SP5 SP4 SP3 SP2 SP1 SP0
(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 can be set as the stack area.
Figure 5-9. Stack Pointer Configuration
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 5-10 and 5-11.
Caution Since RESET input makes SP contents indeterminate, be sure to initialize the SP before
instruction execution.
Figure 5-10. Data to be Saved to Stack Memory
Figure 5-11. Data to be Reset from Stack Memory
Interrupt and
BRK Instruction
PSW
PC15 to PC8
PC15 to PC8
PC7 to PC0 Register Pair Lower
SP SP _ 2
SP _ 2
Register Pair Upper
CALL, CALLF, and
CALLT Instruction PUSH rp Instruction
SP _ 1
SP
SP SP _ 2
SP _ 2
SP _ 1
SP
PC7 to PC0 SP _ 3
SP _ 2
SP _ 1
SP
SP SP _ 3
RETI and RETB
Instruction
PSW
PC15 to PC8 PC15 to PC8
PC7 to PC0 Register Pair Lower
SP SP + 2
SP
Register Pair Upper
RET Instruction POP rp Instruction
SP + 1
PC7 to PC0
SP SP + 2
SP
SP + 1
SP + 2
SP
SP + 1
SP SP + 3