ATTINY20 データシートの表示（PDF） - Atmel Corporation
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ATTINY20 Datasheet PDF : 219 Pages
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Figure 4-2. AVR CPU General Purpose Working Registers
General
Purpose
Working
Registers
7
R16
R16
R17
R17
R18
R18
…
...
R26
R26
R27
R27
R28
R28
R29
R29
R30
R30
R31
R31
0
X-register Low Byte
X-register High Byte
Y-register Low Byte
Y-register High Byte
Z-register Low Byte
Z-register High Byte
Note: A typical implementation of the AVR register file includes 32 general purpose registers but ATtiny20 implements only
16 registers. For reasons of compatibility the registers are numbered R16:R31 and not R0:R15.
Most of the instructions operating on the Register File have direct access to all registers, and most of them are single
cycle instructions.
4.4.1
The X-register, Y-register, and Z-register
Registers R26:R31 have some added functions to their general purpose usage. These registers are 16-bit address
pointers for indirect addressing of the data space. The three indirect address registers X, Y, and Z are defined as
described in Figure 4-3.
Figure 4-3. The X-, Y-, and Z-registers
15
XH
XL
0
X-register
7
07
0
R27
R26
15
YH
YL
0
Y-register
7
07
0
R29
R28
15
ZH
ZL
0
Z-register
7
07
0
R31
R30
In different addressing modes these address registers function as automatic increment and automatic decrement (see
document “AVR Instruction Set” and section “Instruction Set Summary” on page 205 for details).
4.5 Stack Pointer
The stack is mainly used for storing temporary data, local variables and return addresses after interrupts and subroutine
calls. The Stack Pointer registers (SPH and SPL) always point to the top of the stack. Note that the stack grows from
higher memory locations to lower memory locations. This means that the PUSH instructions decreases and the POP
instruction increases the stack pointer value.
ATtiny20 [DATASHEET] 10
Atmel-8235F-AVR-ATtiny20-Datasheet_09/2014
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