Stack Pointer (Sp); Stack Pointer Configuration; Data To Be Saved To Stack Memory; Data To Be Reset From Stack Memory - NEC 78K/0 Series User Manual

2.1.3 Stack pointer (SP)

This is a 16-bit register that holds the start address of the memory stack area. Only the internal high-speed
RAM area 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 2-4 and 2-5.
Caution Since RESET input makes SP contents undefined, be sure to initialize the SP before instruction
execution.
PUSH rp
instruction
SP _ 2
SP
Lower half
SP _ 2
register pairs
Upper half
SP _ 1
register pairs
SP
POP rp
instruction
Lower half
SP
register pairs
Upper half
SP + 1
register pairs
SP SP + 2
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CHAPTER 2 REGISTERS
Figure 2-3. Stack Pointer Configuration
SP
Figure 2-4. Data to Be Saved to Stack Memory
CALL, CALLF and
CALLT instructions
SP _ 2
SP
SP _ 2
SP _ 1
SP
Figure 2-5. Data to Be Reset from Stack Memory
RET instruction
SP
SP + 1
SP SP + 2
User's Manual U12326EJ4V0UM
SP _ 3
SP
SP _ 3
SP _ 2
PC7-PC0
SP _ 1
PC15-PC8
SP
PC7-PC0 SP
PC15-PC8 SP + 1
SP + 2
SP SP + 3
0
Interrupt and
BRK instructions
PC7-PC0
PC15-PC8
PSW
RETI and RETB
instructions
PC7-PC0
PC15-PC8
PSW