ATMEGA48-20PI Atmel, ATMEGA48-20PI Datasheet - Page 12

IC AVR MCU 4K 5V 20MHZ 28-DIP

ATMEGA48-20PI

Manufacturer Part Number
ATMEGA48-20PI
Description
IC AVR MCU 4K 5V 20MHZ 28-DIP
Manufacturer
Atmel
Series
AVR® ATmegar
Datasheets

Specifications of ATMEGA48-20PI

Core Processor
AVR
Core Size
8-Bit
Speed
20MHz
Connectivity
I²C, SPI, UART/USART
Peripherals
Brown-out Detect/Reset, POR, PWM, WDT
Number Of I /o
23
Program Memory Size
4KB (2K x 16)
Program Memory Type
FLASH
Eeprom Size
256 x 8
Ram Size
512 x 8
Voltage - Supply (vcc/vdd)
2.7 V ~ 5.5 V
Data Converters
A/D 6x10b
Oscillator Type
Internal
Operating Temperature
-40°C ~ 85°C
Package / Case
28-DIP (0.300", 7.62mm)
Lead Free Status / RoHS Status
Contains lead / RoHS non-compliant
Other names
ATMEGA48-24PI
ATMEGA48-24PI
6.5.1
6.6
12
Stack Pointer
ATmega48/88/168
The X-register, Y-register, and Z-register
The registers R26..R31 have some added functions to their general purpose usage. These reg-
isters 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 6-3.
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).
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 Pointer Register always points
to the top of the Stack. Note that the Stack is implemented as growing from higher memory loca-
tions to lower memory locations. This implies that a Stack PUSH command decreases the Stack
Pointer.
The Stack Pointer points to the data SRAM Stack area where the Subroutine and Interrupt
Stacks are located. This Stack space in the data SRAM must be defined by the program before
any subroutine calls are executed or interrupts are enabled. The Stack Pointer must be set to
point above 0x0100, preferably RAMEND. The Stack Pointer is decremented by one when data
is pushed onto the Stack with the PUSH instruction, and it is decremented by two when the
return address is pushed onto the Stack with subroutine call or interrupt. The Stack Pointer is
incremented by one when data is popped from the Stack with the POP instruction, and it is incre-
mented by two when data is popped from the Stack with return from subroutine RET or return
from interrupt RETI.
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 implementa-
tions of the AVR architecture is so small that only SPL is needed. In this case, the SPH Register
will not be present.
X-register
Y-register
Z-register
The X-, Y-, and Z-registers
15
7
R27 (0x1B)
15
7
R29 (0x1D)
15
7
R31 (0x1F)
XH
YH
ZH
0
0
0
7
R26 (0x1A)
7
R28 (0x1C)
7
R30 (0x1E)
Figure
6-3.
XL
YL
ZL
0
2545S–AVR–07/10
0
0
0
0
0

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