AT89C55WD datasheet(17/35 Pages) ATMEL

17 / 35 page

1921C–MICRO–3/05

AT89C55WD

The Timer 0 and Timer 1 flags, TF0 and TF1, are set at S5P2 of the cycle in which the timers

overflow. The values are then polled by the circuitry in the next cycle. However, the Timer 2 flag,

TF2, is set at S2P2 and is polled in the same cycle in which the timer overflows.

Figure 15-1. Interrupt Sources

Table 15-1.

Interrupt Enable (IE) Register

(MSB)

(LSB)

–

ET2

ET1

EX1

ET0

EX0

Enable Bit = 1 enables the interrupt.

Enable Bit = 0 disables the interrupt.

Symbol

Position

Function

IE.7

Disables all interrupts. If EA = 0, no interrupt is acknowledged. If EA

= 1, each interrupt source is individually enabled or disabled by

setting or clearing its enable bit.

–

IE.6

Reserved.

ET2

IE.5

Timer 2 interrupt enable bit.

IE.4

Serial Port interrupt enable bit.

ET1

IE.3

Timer 1 interrupt enable bit.

EX1

IE.2

External interrupt 1 enable bit.

ET0

IE.1

Timer 0 interrupt enable bit.

EX0

IE.0

External interrupt 0 enable bit.

User software should never write 1s to reserved bits, because they may be used in future AT89

products.

IE1

IE0

TF1

TF0

INT1

INT0

TF2

EXF2

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