Atmel AT90S2333-8AC, Manual

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AT90S/LS2333 and AT90S/LS4433
19
$00e MAIN: ldi r16,low(RAMEND); Main program start
$00f out SP,r16;
$010 <instr> xxx ;
… … … …
Reset Sources
The AT90S2333/4433 has four 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.
• Brown-Out Reset. The MCU is reset when the supply voltage V
CC
falls below a certain voltage.
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 pro-
gram 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 and Table 5 define the timing and electrical
parameters of the reset circuitry.
Figure 24. Reset Logic
Note: The Power-On Reset will not work unless the supply voltage has been below Vpot (falling).
Table 4. Reset Characteristics (V
CC
= 5.0V)
Symbol Parameter Min Typ Max Units
V
POT
Power-On Reset Threshold Voltage,
rising
1.0 1.4 1.8 V
Power-On Reset Threshold Voltage,
falling
0.4 0.6 0.8 V
V
RST
RESET Pin Threshold Voltage 0.6V
CC
V
V
BOT
Brown-Out Reset Threshold Voltage
2.6 (BODLEVEL = 1) 2.7 (BODLEVEL = 1) 2.8 (BODLEVEL = 1)
V
3.8 (BODLEVEL = 0) 4.0 (BODLEVEL = 0) 4.2 (BODLEVEL = 0)
MCU Status
Register (MCUSR)
Brown-Out
Reset Circuit
BODEN
BODLEVEL
Delay Counters
CKSEL[2:0]
CK
Full
WDRF
BORF
EXTRF
PORF
DATA BUS