P89C51RB2BA datasheet(19/52 Pages) PHILIPS

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Philips Semiconductors

Preliminary specification

89C51RB2/89C51RC2/

89C51RD2

80C51 8-bit Flash microcontroller family

16KB/32KB/64KB ISP/IAP Flash with 512B/512B/1KB RAM

1999 Sep 23

Interrupt Priority Structure

The 89C51RB2/RC2/RD2 has an 8 source four-level interrupt

structure (see Table 7).

There are 3 SFRs associated with the four-level interrupt. They are

the IE, IP, and IPH. (See Figures 10, 11, and 12.) The IPH (Interrupt

Priority High) register makes the four-level interrupt structure

possible. The IPH is located at SFR address B7H. The structure of

the IPH register and a description of its bits is shown in Figure 12.

The function of the IPH SFR is simple and when combined with the

IP SFR determines the priority of each interrupt. The priority of each

interrupt is determined as shown in the following table:

PRIORITY BITS

INTERRUPT PRIORITY LEVEL

IPH.x

IP.x

INTERRUPT PRIORITY LEVEL

Level 0 (lowest priority)

Level 1

Level 2

Level 3 (highest priority)

The priority scheme for servicing the interrupts is the same as that

for the 80C51, except there are four interrupt levels rather than two

as on the 80C51. An interrupt will be serviced as long as an interrupt

of equal or higher priority is not already being serviced. If an

interrupt of equal or higher level priority is being serviced, the new

interrupt will wait until it is finished before being serviced. If a lower

priority level interrupt is being serviced, it will be stopped and the

new interrupt serviced. When the new interrupt is finished, the lower

priority level interrupt that was stopped will be completed.

Table 7.

Interrupt Table

SOURCE

POLLING PRIORITY

REQUEST BITS

HARDWARE CLEAR?

VECTOR ADDRESS

IE0

N (L)1

Y (T)2

03H

TP0

0BH

IE1

N (L)

Y (T)

13H

TF1

1BH

PCA

CF, CCFn

n = 0–4

33H

RI, TI

23H

TF2, EXF2

2BH

NOTES:

1. L = Level activated

2. T = Transition activated

EX0

IE (0A8H)

Enable Bit = 1 enables the interrupt.

Enable Bit = 0 disables it.

BIT

SYMBOL

FUNCTION

IE.7

Global disable bit. If EA = 0, all interrupts are disabled. If EA = 1, each interrupt can be individually

enabled or disabled by setting or clearing its enable bit.

IE.6

PCA interrupt enable bit

IE.5

ET2

Timer 2 interrupt enable bit.

IE.4

Serial Port interrupt enable bit.

IE.3

ET1

Timer 1 interrupt enable bit.

IE.2

EX1

External interrupt 1 enable bit.

IE.1

ET0

Timer 0 interrupt enable bit.

IE.0

EX0

External interrupt 0 enable bit.

SU01290

ET0

EX1

ET1

ET2

Figure 10. IE Registers

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