Preliminary W78E51B
1. INT2 / INT3
Two additional external interrupts, INT2 and INT3 , whose functions are similar to those of external
interrupt 0 and 1 in the standard 80C52. The functions/status of these interrupts are
determined/shown by the bits in the XICON (External Interrupt Control) register. The XICON register
is bit-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 SEQUENCE WITHIN
PRIORITY LEVEL
POLLING
ENABLE
REQUIRED
SETTINGS
INTERRUPT
TYPE
EDGE/LEVEL
External Interrupt 0
Timer/Counter 0
External Interrupt 1
Timer/Counter 1
Serial Port
03H
0BH
13H
1BH
23H
33H
3BH
0 (highest)
IE.0
TCON.0
1
IE.1
-
2
IE.2
TCON.2
3
IE.3
-
4
IE.4
-
External Interrupt 2
External Interrupt 3
5
XICON.2
XICON.6
XICON.0
XICON.3
6 (lowest)
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
alternative function pins. It can be used as general I/O pins or external interrupt input sources (INT2 ,
INT3 ).
Example:
P4
REG 0D8H
P4, #0AH
A, P4
P4.0
P4.1
MOV
MOV
SETB
CLR
; Output data "A" through P4.0- P4.3.
; Read P4 status to Accumulator.
; Set bit P4.0
; Clear bit P4.1
Publication Release Date: December 1998
Revision A1
- 5 -
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