Datasheet

Figure 7-3. 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
Instruction Set Summary on page 419
7.5. Stack Pointer
The Stack is mainly used for storing temporary data, for storing local variables and for storing 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 7-1. 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
The AVR Stack Pointer is implemented as two 8-bit registers in the I/O space. The number of bits actually
used is implementation dependent. Note that the data space in some implementations of the AVR
architecture is so small that only SPL is needed. In this case, the SPH Register will not be present.
Atmel ATmega16M1/32M1/64M1 [DATASHEET]
Atmel-8209F-ATmega16M1/32M1/64M1_Datasheet_Complete-10/2016
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