Atmel AT85DVK-07 Especificaciones descargar pdf (Pagina 24)

AT85C51SND3Bx

7632A–MP3–03/06

Figure 13. Reset Circuitry and Power-On Reset

Cold Reset 2 conditions are required before enabling a CPU start-up:

•V

must reach the specified V

range

• The level on X1 input pin must be outside the specification (V

, V

)

If one of these 2 conditions are not met, the microcontroller does not start correctly and

can execute an instruction fetch from anywhere in the program space. An active level

applied on the

RST pin must be asserted till both of the above conditions are met. A

reset is active when the level V

is reached and when the pulse width covers the period

of time where V

and the oscillator are not stabilized. 2 parameters have to be taken

into account to determine the reset pulse width:

•V

rise time,

• Oscillator startup time.

To determine the capacitor value to implement, the highest value of these 2 parameters

has to be chosen.

Warm Reset To achieve a valid reset, the reset signal must be maintained for at least 2 machine

cycles (24 oscillator clock periods) while the oscillator is running. The number of clock

periods is mode independent (X2 or X1).

Watchdog Timer Reset As detailed in Section “Watchdog Timer”, page 75, the WDT generates a 96-clock

period pulse on the RST pin. In order to properly propagate this pulse to the rest of the

application in case of external capacitor or power-supply supervisor circuit, a 1 kΩ resis

tor must be added as shown in Figure 14.

Figure 14. Reset Circuitry for WDT Reset-out Usage

Power Fail Detector The Power Fail Detector (PFD) ensures that whole product is in reset when internal volt-

age is out of its limits specification. PFD limits are detailed in the Section “DC

Characteristics”, page 241.

RST

IOVDD

IOVSS

To CPU Core

and Peripherals

RST

IOVSS

Power-on ResetRST input circuitry

From Internal

Reset Source

RST

IOVDD

To CPU Core

and Peripherals

IOVSS

From WDT

Reset Source

To Other

On-board

Circuitry

1 2 ... 19 20 21 22 23 24 25 26 27 28 29 ... 262 263

Atmel AT85DVK-07 Especificaciones Pagina 24

Comentarios a estos manuales

Atmel AT85DVK-07 Especificaciones Pagina 24

Comentarios a estos manuales

Relacionado con productos y manuales para Redes Atmel AT85DVK-07