Atmel AT85DVK-07 Especificaciones descargar pdf (Pagina 58)

AT85C51SND3Bx

7632A–MP3–03/06

External Interrupts

INT1:0 Inputs External interrupts INT0 and INT1 (INTn, n = 0 or 1) pins may each be programmed to

be level-triggered or edge-triggered, dependent upon bits IT0 and IT1 (

ITn, n = 0 or 1) in

TCON register as shown in

INT1:0 Input Circuitry. If ITn = 0, INTn is triggered by a low

level at the pin. If ITn = 1, INTn is negative-edge triggered. External interrupts are

enabled with bits EX0 and EX1 (

EXn, n = 0 or 1) in IEN0. Events on INTn set the inter-

rupt request flag IEn in TCON register. If the interrupt is edge-triggered, the request flag

is cleared by hardware when vectoring to the interrupt service routine. If the interrupt is

level-triggered, the interrupt service routine must clear the request flag and the interrupt

must be de-asserted before the end of the interrupt service routine.

INT0 and INT1 inputs provide both the capability to exit from Power-down mode on low

level signals as detailed in

Section “Exiting Power-down Mode”, page 21.

Figure 29. INT1:0 Input Circuitry

KIN3:0 Inputs External interrupts KIN0 to KIN3 provide the capability to connect a matrix keyboard. For

detailed information on these inputs, refer to

Section “Keyboard Interface”, page 239.

Input Sampling External interrupt pins (INT1:0 and KIN3:0) are sampled once per peripheral cycle (6

peripheral clock periods) (see

Minimum Pulse Timings). A level-triggered interrupt pin

held low or high for more than 6 peripheral clock periods (12 oscillator in standard mode

or 6 oscillator clock periods in X2 mode) guarantees detection. Edge-triggered external

interrupts must hold the request pin low for at least 6 peripheral clock periods.

Figure 30. Minimum Pulse Timings

INT0/1

IT0/1

TCON.0/2

EX0/1

IEN0.0/2

INT0/1

Interrupt

Request

IE0/1

TCON.1/3

Edge-Triggered Interrupt

Level-Triggered Interrupt

1 cycle 1 cycle

> 1 Peripheral Cycle

1 cycle

> 1 Peripheral Cycle

1 2 ... 53 54 55 56 57 58 59 60 61 62 63 ... 262 263

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