ATmega48 Automotive Atmel Corporation, ATmega48 Automotive Datasheet - Page 11

• Manufacturer Part Number: ATmega48 Automotive
• Manufacturer: Atmel Corporation

Specifications of ATmega48 Automotive

• Flash (kbytes): 4 Kbytes
• Pin Count: 32
• Max. Operating Frequency: 16 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 12
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 23
• Ext Interrupts: 24
• Usb Speed: No
• Usb Interface: No
• Spi: 2
• Twi (i2c): 1
• Uart: 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 8
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: No
• Crypto Engine: No
• Sram (kbytes): 0.5
• Eeprom (bytes): 256
• Self Program Memory: NO
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• Temp. Range (deg C): -40 to 125
• I/o Supply Class: 2.7 to 5.5
• Operating Voltage (vcc): 2.7 to 5.5
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 3
• Output Compare Channels: 6
• Input Capture Channels: 1
• Pwm Channels: 6
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

4.5.1
4.6
7530I–AVR–02/10
Stack Pointer
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 4-3.
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
Bit
Read/Write
Initial Value
RAMEND
RAMEND
SP15
The X-, Y-, and Z-registers
SP7
R/W
R/W
15
7
15
7
R27 (0x1B)
15
7
R29 (0x1D)
15
7
R31 (0x1F)
RAMEND
RAMEND
SP14
R/W
R/W
SP6
14
6
RAMEND
RAMEND
SP13
SP5
R/W
R/W
13
5
XH
YH
ZH
0
ATmega48/88/168 Automotive
RAMEND
RAMEND
SP12
R/W
SP4
R/W
12
4
RAMEND
RAMEND
SP11
SP3
R/W
R/W
11
3
0
0
Figure
7
R26 (0x1A)
7
R28 (0x1C)
7
R30 (0x1E)
RAMEND
RAMEND
SP10
SP2
R/W
R/W
10
2
4-3.
RAMEND
RAMEND
R/W
R/W
SP9
SP1
9
1
XL
YL
ZL
0
RAMEND
RAMEND
SP8
SP0
R/W
R/W
8
0
SPH
SPL
11
0
0
0
0
0