AT90LS4433-4AI datasheet(20/126 Pages) ATMEL

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AT90S/LS4433

1042H–AVR–04/03

Stack Pointer – SP

The AT90S4433 Stack Pointer is implemented as an 8-bit register in the I/O space loca-

tion $3D ($5D). As the AT90S4433 data memory has $0DF locations, eight bits are

used.

The Stack Pointer points to the data SRAM stack area where the Subroutine and Inter-

rupt 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 $60. 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 an address is pushed onto the Stack with subroutine calls and interrupts. The

Stack Pointer is incremented by one when data is popped from the stack with the POP

instruction, and it is incremented by two when an address is popped from the Stack with

return from subroutine RET or return from interrupt RETI.

Reset and Interrupt

Handling

The AT90S4433 provides 13 different interrupt sources. These interrupts and the sepa-

rate reset vector each have a separate Program Vector in the Program memory space.

All interrupts are assigned individual enable bits, which must be set (one) together with

the I-bit in the Status Register in order to enable the interrupt.

The lowest addresses in the Program memory space are automatically defined as the

Reset and Interrupt Vectors. The complete list of Vectors is shown in Table 3. The list

also determines the priority levels of the different interrupts. The lower the address, the

higher the priority level. RESET has the highest priority, and next is INT0 (the External

Interrupt Request 0), etc.

765

432

$3D ($5D)

SP7

SP6

SP5

SP4

SP3

SP2

SP1

SP0

Read/Write

R/W

Initial Value

Table 3. Reset and Interrupt Vectors

Vector No.

Program

Address

Source

Interrupt Definition

$000

RESET

External Pin, Power-on Reset, Brown-out Reset

and Watchdog Reset

$001

INT0

External Interrupt Request 0

$002

INT1

External Interrupt Request 1

$003

TIMER1 CAPT

Timer/Counter1 Capture Event

$004

TIMER1 COMP

Timer/Counter1 Compare Match

$005

TIMER1 OVF

Timer/Counter1 Overflow

$006

TIMER0 OVF

Timer/Counter0 Overflow

$007

SPI, STC

Serial Transfer Complete

$008

UART, RX

UART, Rx Complete

$009

UART, UDRE

UART Data Register Empty

$00A

UART, TX

UART, Tx Complete

$00B

ADC

ADC Conversion Complete

$00C

EE_RDY

EEPROM Ready

$00D

ANA_COMP

Analog Comparator

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