Preliminary W78LE51

Publication Release Date: December 1998

- 5 -

Revision A1

addressable but is not a standard register in the standard 80C52. Its address is at 0C0H. To set/clear

bits in the XICON register, one can use the "SETB (/CLR) bit" instruction. For example, "SETB 0C2H"

sets the EX2 bit of XICON.

XICON - external interrupt control (C0H)

PX3

EX3

IE3

IT3

PX2

EX2

IE2

IT2

PX3: External interrupt 3 priority high if set

EX3: External interrupt 3 enable if set

IE3: If IT3 = 1, IE3 is set/cleared automatically by hardware when interrupt is detected/serviced

IT3: External interrupt 3 is falling-edge/low-level triggered when this bit is set/cleared by software

PX2: External interrupt 2 priority high if set

EX2: External interrupt 2 enable if set

IE2: If IT2 = 1, IE2 is set/cleared automatically by hardware when interrupt is detected/serviced

IT2: External interrupt 2 is falling-edge/low-level triggered when this bit is set/cleared by software

Eight-source interrupt informations:

INTERRUPT

SOURCE

VECTOR

ADDRESS

POLLING

SEQUENCE WITHIN

PRIORITY LEVEL

ENABLE

REQUIRED

SETTINGS

INTERRUPT

TYPE

EDGE/LEVEL

External Interrupt 0

03H

0 (highest)

IE.0

TCON.0

Timer/Counter 0

0BH

1

IE.1

-

External Interrupt 1

13H

2

IE.2

TCON.2

Timer/Counter 1

1BH

3

IE.3

-

Serial Port

23H

4

IE.4

-

External Interrupt 2

33H

5

XICON.2

XICON.0

External Interrupt 3

3BH

6 (lowest)

XICON.6

XICON.3

2. PORT4

Another bit-addressable port P4 is also available and only 4 bits (P4<3:0>) can be used. This port

address is located at 0D8H with the same function as that of port P1, except the P4.3 and P4.2 are

INT3 ).

Example:

P4

REG

0D8H

MOV

P4, #0AH

; Output data "A" through P4.0

−P4.3.

MOV

A, P4

; Read P4 status to Accumulator.

SETB

P4.0

; Set bit P4.0

CLR

P4.1

; Clear bit P4.1

3. Reduce EMI Emission

Because of on-chip MTP-ROM, when a program is running in internal ROM space, the ALE will be

unused. The transition of ALE will cause noise, so it can be turned off to reduce the EMI emission if it