AT90S8515 Просмотр технического описания (PDF) - Atmel Corporation

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AT90S8515

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

Atmel Corporation 

Reset Sources

AT90S8515

$00f

$010

$011

ldi r16,low(RAMEND)

out SPL,r16

<instr> xxx

…

…

…

…

The AT90S8515 has three 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

more than 50 ns.

• Watchdog Reset. The MCU is reset when the Watchdog timer period expires and

the Watchdog is enabled.

During reset, all I/O registers are set to their initial values and the program starts execu-

tion from address $000. The instruction placed in address $000 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 23 shows the reset logic. Table 3

defines the timing and electrical parameters of the reset circuitry.

Figure 23. Reset Logic

0841G–09/01

Table 3. Reset Characteristics

Symbol Parameter

Min Typ Max Units

VPOT(Not

e:)

Power-on Reset Threshold Voltage (rising)

Power-on Reset Threshold Voltage (falling)

0.8 1.2

1.6

V

0.2 0.4

0.6

V

VRST

tTOUT

RESET Pin Threshold Voltage

Reset Delay Time-out Period FSTRT

Unprogrammed

–

– 0.9 VCC

V

11.0 16.0 21.0

ms

tTOUT

Reset Delay Time-out Period FSTRT

Programmed

0.25 0.28 0.31

ms

Note: The Power-on Reset will not work unless the supply voltage has been below VPOT

(falling).

23

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