AT90S1200 ATMEL Corporation, AT90S1200 Datasheet - Page 12

• Manufacturer Part Number: AT90S1200
• Description: 8-Bit Microcontroller with 1K bytes In-System Programmable Flash
• Manufacturer: ATMEL Corporation

Reset and Interrupt
Handling
Reset Sources
12
AT90S1200
The AT90S1200 provides three different interrupt sources. These interrupts and the
separate reset vector, each have a separate program vector in the program memory
space. All the interrupts are assigned individual enable bits that 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 2. The list
also determines the priority levels of the different interrupts. The lower the address the
higher is the priority level. RESET has the highest priority, and next is INT0 (the External
Interrupt Request 0), etc.
Table 2. Reset and Interrupt Vectors
The most typical and general program setup for the Reset and Interrupt Vector
Addresses are:
The AT90S1200 has three sources of reset:
•
•
•
During Reset, all I/O registers are then set to their initial values, and the program starts
execution from address $000. The instruction 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 13 shows the reset logic. Table 3
defines the timing and electrical parameters of the reset circuitry. Note that Power-on
Reset timing is clocked by the internal RC Oscillator. Refer to characterization data for
RC Oscillator frequency at other V
Vector No.
Address
$000
$001
$002
$003
;
$004
Power-on Reset. The MCU is reset when the supply voltage is below the power-on
Reset threshold (V
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.
1
2
4
5
…
Labels
MAIN:
Program Address
…
$000
$001
$002
$003
POT
Code
rjmp
rjmp
rjmp
rjmp
<instr>
).
…
xxx
TIMER0, OVF0
CC
RESET
EXT_INT0
TIM0_OVF
ANA_COMP
…
ANA_COMP
voltages.
Source
RESET
INT0
Watchdog Reset
Comments
; Reset Handler
; IRQ0 Handler
; Timer0 Overflow Handler
; Analog Comparator Handler
; Main program start
Hardware Pin, Power-on Reset and
External Interrupt Request 0
Timer/Counter0 Overflow
Analog Comparator
Interrupt Definition
0838H–AVR–03/02