Rainbow-electronics ATtiny12 Manual do Utilizador descarregar pdf (Página 18)

ATtiny11/12

1006C–09/01

Power-on Reset for the

ATtiny11

A Power-on Reset (POR) circuit ensures that the device is reset from power-on. As

shown in Figure 16, an internal timer is clocked from the watchdog timer. This timer pre-

vents the MCU from starting a certain period after V

has reached the Power-on

Threshold Voltage – V

POT

. See Figure 18. The total reset period is the Delay Time-out

period – t

TOUT

. The FSTRT fuse bit in the Flash can be programmed to give a shorter

start-up time.The start-up times for the different clock options are shown in the following

table. The Watchdog Oscillator is used for timing the start-up time, and this oscillator is

voltage dependent as shown in the section “ATtiny11 Typical Characteristics” on page

58.

If the built-in start-up delay is sufficient, RESET

can be connected to V

directly or via

an external pull-up resistor. By holding the RESET

pin low for a period after V

has

been applied, the Power-on Reset period can be extended. Refer to Figure 19 for a tim-

ing example on this.

Table 7. Start-up Times for the ATtiny11 (V

= 2.7V)

Selected Clock Option

Start-up Time t

TOUT

FSTRT Unprogrammed FSTRT Programmed

External Crystal 67 ms 4.2 ms

External Ceramic Resonator 67 ms 4.2 ms

External Low-frequency Crystal 4.2 s 4.2 s

External RC Oscillator 4.2 ms 67 µs

Internal RC Oscillator 4.2 ms 67 µs

External Clock 4.2 ms

5 clocks from reset,

2 clocks from power-down

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 85 86

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Rainbow-electronics ATtiny12 Manual do Utilizador Página 18