AT89C51ED2-RDTUM datasheet(73/137 Pages) ATMEL

73 / 137 page

4235K–8051–05/08

AT89C51RD2/ED2

17.1

Registers

The PCA interrupt vector is located at address 0033H, the SPI interrupt vector is located at

address 004BH and Keyboard interrupt vector is located at address 003BH. All other vectors

addresses are the same as standard C52 devices.

Table 17-1.

Priority Level Bit Values

A low-priority interrupt can be interrupted by a high priority interrupt, but not by another low-prior-

ity interrupt. A high-priority interrupt can’t be interrupted by any other interrupt source.

If two interrupt requests of different priority levels are received simultaneously, the request of

higher priority level is serviced. If interrupt requests of the same priority level are received simul-

taneously, an internal polling sequence determines which request is serviced. Thus within each

priority level there is a second priority structure determined by the polling sequence.

17.2

Interrupt Sources and Vector Addresses

Table 17-2.

Interrupt Sources and Vector Addresses

IPH.x

IPL.x

Interrupt Level Priority

0 (Lowest)

3 (Highest)

Number

Polling Priority

Interrupt Source

Interrupt

Request

Vector

Address

Reset

0000h

INT0

IE0

0003h

Timer 0

TF0

000Bh

INT1

IE1

0013h

Timer 1

IF1

001Bh

UART

RI+TI

0023h

Timer 2

TF2+EXF2

002Bh

PCA

CF + CCFn (n = 0 - 4)

0033h

Keyboard

KBDIT

003Bh

0043h

SPI

SPIIT

004Bh

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