AT90LS2343 ATMEL [ATMEL Corporation], AT90LS2343 Datasheet - Page 20

• Manufacturer Part Number: AT90LS2343
• Description: 8-Bit Microcontroller with 2K Bytes of In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Reset Sources
20
AT90S/LS2323/2343
The most typical program setup for the Reset and Interrupt vector addresses are:
The AT90S2323/2343 provides three sources of reset:
•
•
•
During reset, all I/O registers are set to their initial values and the program starts execu-
tion 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 24 shows the reset logic.
Table 4 defines the timing and electrical parameters of the reset circuitry.
Figure 24. Reset Logic
The AT90S/LS2323 has a programmable start-up time. A fuse bit (FSTRT) in the Flash
memory selects the shortest start-up time when programmed (“0”). The AT90S/LS2323
is shipped with this bit unprogrammed.
The AT90S/LS2343 has a fixed start-up time.
RESET
VCC
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.
Address
$000
$001
$002
$003
...
100 - 500K
Power-On Reset
Reset Circuit
RC-Oscillator
Labels
MAIN:
...
Watchdog
On-Chip
Circuit
Timer
POT
).
Code
rjmp RESET
rjmp EXT_INT0
rjmp TIM_OVF0
ldi r16, low(RAMEND)
out SPL, r16
<instr> xxx
...
Q0
POR
14-Stage Ripple Counter
Q3
Comments
; Reset Handler
; IRQ0 Handler
; Timer0 Overflow
; Handler;
...
; Main program start
Q13
S
R
Q
Q
1004D–09/01