attiny13-20ss ATMEL Corporation, attiny13-20ss Datasheet - Page 30

• Manufacturer Part Number: attiny13-20ss
• Description: 8-bit Microcontroller With 1k Bytes In-system Programmable Flash - Atmel Corporation
• Manufacturer: ATMEL Corporation

System Control and
Reset
Resetting the AVR
Reset Sources
30
ATtiny13
During reset, all I/O Registers are set to their initial values, and the program starts exe-
cution from the Reset Vector. The instruction placed at the Reset Vector must be a
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 12 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 different selections for the delay period are presented in “Clock
Sources” on page 22.
The ATtiny13 has four sources of reset:
•
•
•
•
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
longer than the minimum pulse length.
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
Brown-out Reset threshold (V
POT
).
BOT
) and the Brown-out Detector is enabled.
CC
is below the
2535G–AVR–01/07