AT90S2313-4PI 查看數據表（PDF） - Atmel Corporation

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AT90S2313-4PI

8-bit Microcontroller with 2K Bytes of In-System Programmable Flash

Atmel Corporation 

Power-on Reset

Table 4. Number of Watchdog Oscillator Cycles

FSTRT

Programmed

Time-out at VCC = 5V

0.28 ms

Unprogrammed

16.0 ms

Number of WDT Cycles

256

16K

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

shown in Figure 23, an internal timer is clocked from the Watchdog Timer. This timer

prevents the MCU from starting until after a certain period after VCC has reached the

Power-on Threshold voltage (VPOT) (see Figure 24). The FSTRT Fuse bit in the Flash

can be programmed to give a shorter start-up time if a ceramic resonator or any other

fast-start Oscillator is used to clock the MCU.

If the built-in start-up delay is sufficient, RESET can be connected to VCC directly or via

an external pull-up resistor. By holding the RESET pin low for a period after VCC has

been applied, the Power-on Reset period can be extended. Refer to Figure 25 for a tim-

ing example of this.

Figure 24. MCU Start-up, RESET Tied to VCC.

VCC

VPOT

RESET

VRST

TIME-OUT

tTOUT

INTERNAL

RESET

Figure 25. MCU Start-up, RESET Controlled Externally

VCC

VPOT

RESET

VRST

TIME-OUT

tTOUT

INTERNAL

RESET

20 AT90S2313

0839I–AVR–06/02

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