Datasheet

Figure 11-3. The X-, Y-, and Z-registers
15
XH
XL
0
X-register
7
0
7
0
R27
R26
15
YH
YL
0
Y-register
7
0
7
0
R29
R28
15
ZH
ZL
0
Z-register
7
0
7
0
R31
R30
In the different addressing modes, these address registers have functions as fixed displacement,
automatic increment, and automatic decrement (see the instruction set reference for details).
Related Links
36. Instruction Set Summary
11.5 Stack Pointer
The stack is mainly used for storing temporary data, local variables, and return addresses after interrupts
and subroutine calls. The stack is implemented as growing from higher to lower memory locations. The
Stack Pointer register always points to the top of the stack.
The stack pointer points to the data SRAM stack area where the subroutine and interrupt stacks are
located. A stack PUSH command will decrease the stack pointer. The stack in the data SRAM must be
defined by the program before any subroutine calls are executed or interrupts are enabled. Initial stack
pointer value equals the last address of the internal SRAM and the stack pointer must be set to point
above start of the SRAM. See the table for stack pointer details.
Table 11-1. Stack Pointer Instructions
Instruction Stack Pointer Description
PUSH
Decremented by 1 Data is pushed onto the stack
CALL
ICALL
RCALL
Decremented by 2 Return address is pushed onto the stack with a subroutine call or
interrupt
POP
Incremented by 1 Data is popped from the stack
RET
RETI
Incremented by 2 Return address is popped from the stack with return from subroutine or
return from interrupt
ATmega48PA/88PA/168PA
AVR CPU Core
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40002011A-page 33