
33
2543L–AVR–08/10
ATtiny2313
System Control
and Reset
Resetting the AVR
During reset, all I/O Registers are set to their initial values, and the program starts execution
from the Reset Vector. The instruction placed at the Reset Vector 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 14 shows the reset logic.
Table 15 defines the electrical
parameters of the reset circuitry.
The I/O ports of the AVR are immediately reset to their initial state when a reset source goes
active. This does not require any clock source to be running.
After all reset sources have gone inactive, a delay counter is invoked, stretching the internal
reset. This allows the power to reach a stable level before normal operation starts. The time-out
period of the delay counter is defined by the user through the SUT and CKSEL Fuses. The dif-
Reset Sources
The ATtiny2313 has four sources of reset:
Power-on Reset. The MCU is reset when the supply voltage is below the Power-on Reset
threshold (VPOT).
External Reset. The MCU is reset when a low level is present on the RESET pin for longer
than the minimum pulse length.
Watchdog Reset. The MCU is reset when the Watchdog Timer period expires, the Watchdog
is enabled, and Watchdog Interrupt is disabled.
Brown-out Reset. The MCU is reset when the supply voltage VCC is below the Brown-out
Reset threshold (VBOT) and the Brown-out Detector is enabled.
Figure 14. Reset Logic
MCU Status
Register (MCUSR)
Brown-out
Reset Circuit
BODLEVEL [2..0]
Delay Counters
CKSEL[3:0]
CK
TIMEOUT
WDRF
BORF
EXTRF
PORF
DATA BUS
Clock
Generator
SPIKE
FILTER
Pull-up Resistor
Watchdog
Oscillator
SUT[1:0]
Power-on Reset
Circuit