Atmel AVR AT90LS4434, Preliminary

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AT90S/LS4434 and AT90S/LS8535
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The most typical and general program setup for the Reset and Interrupt vector addresses are:
Address Labels Code Comments
$000 rjmp RESET ; Reset Handler
$001 rjmp EXT_INT0 ; IRQ0 Handler
$002 rjmp EXT_INT1 ; IRQ1 Handler
$003 rjmp TIM2_COMP ; Timer2 Compare Handler
$004 rjmp TIM2_OVF ; Timer2 Overflow Handler
$005 rjmp TIM1_CAPT ; Timer1 Capture Handler
$006 rjmp TIM1_COMPA ; Timer1 CompareA Handler
$007 rjmp TIM1_COMPB ; Timer1 CompareB Handler
$008 rjmp TIM1_OVF ; Timer1 Overflow Handler
$009 rjmp TIM0_OVF ; Timer0 Overflow Handler
$00a rjmp SPI_STC; ; SPI Transfer Complete Handler
$00b rjmp UART_RXC ; UART RX Complete Handler
$00c rjmp UART_DRE ; UDR Empty Handler
$00d rjmp UART_TXC ; UART TX Complete Handler
$00e rjmp ADC ; ADC Conversion Complete Interrupt Handler
$00f rjmp EE_RDY ; EEPROM Ready Handler
$010 rjmp ANA_COMP ; Analog Comparator Handler
$011 MAIN: ldi r16, high(RAMEND); Main program start
$012 out SPH,r16
$013 ldi r16, low(RAMEND);
$014 out SPL,r16
$015 <instr> xxx
… … … …
Reset Sources
The AT90S4434/8535 has three sources of reset:
• Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset threshold (V
POT
).
• External Reset. The MCU is reset when a low level is present on the RESET pin for more than 50 ns.
• Watchdog Reset. The MCU is reset when the Watchdog timer period expires and the Watchdog is enabled.
During reset, all I/O registers are set to their initial values and the program starts execution from address $000. The instruc-
tion placed in address $000 must be an RJMP (relative jump) instruction to the reset handling routine. If the program never
enables an interrupt source, the interrupt vectors are not used and regular program code can be placed at these locations.
The circuit diagram in Figure 23 shows the reset logic. Table 4 defines the timing and electrical parameters of the reset
circuitry.
Figure 23. Reset Logic