8051 chap6 interrupts VI XỬ LÝ

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The 8051 Microcontroller
Chapter 6
Interrupts
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Ref. I. Scott Mackenzie, The 8051 Microcontroller

What Is an Interrupt?

(Source: />
• An interrupt = Occurrence of a condition (an event)
• Deal with the event while another program is executing
• Do many things “simultaneously”
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Interrupts

Hardware
Event

When an interrupt occurs, the main program temporarily suspends
execution and branches to the interrupt service routine (ISR),
perform the operation, and terminates with a “return from
interrupt” instruction (RETI).
Ref. I. Scott Mackenzie

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ISR vs. Subroutine
• Similarity: CPU executes another program and then returns to
the original program.
• Difference: It is NOT known when the main program suspends
execution.
ISR_NAME:
…
…
RETI

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SUBROUTINE_NAME:
…
…
RET

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Interrupt Sources
• 2 External Interrupts
• 2 Timer Interrupts
• 1 Serial Port Interrupt
• Timer 2 Interrupt (8052 only)

Ref. I. Scott Mackenzie

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When an Interrupt occurs?

An interrupt = Occurrence of a condition (an event)

•
•
•
•
•

When a falling edge occur at /INT0 pin, External 0 Interrupt occurs.
When a falling edge occur at /INT1 pin, External 1 Interrupt occurs.
When Timer 0 is overflow, Timer 0 Interrupt occurs.
When Timer 1 is overflow, Timer 1 Interrupt occurs.
When the transmission is done (transmit buffer is empty) or the
reception is done (receiver buffer is full), Serial Port Interrupt
occurs.

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Interrupt Sources

2 external interrupts (/INT0 and /INT1), 2 timer interrupts (TF0 and TF1), a
serial port interrupt (RI or TI), and Timer 2 interrupt (8052 only)
Ref. I. Scott Mackenzie

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Enabling and Disabling Interrupts
EA

-

ET2 ES ET1 EX1 ET0 EX0

IE (Interrupt Enable) Register
•
•
•
•
•
•
•
•

EA : Global enable/disable
- : Undefined

ET2: Enable Timer 2 interrupt
ES: Enable Serial port interrupt
ET1: Enable Timer 1 interrupt
EX1: Enable External 1 interrupt
ET0: Enable Timer 0 interrupt
EX0: Enable External 0 interrupt
1 = Enable; 0 = Disable

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Enabling and Disabling Interrupts
EA

-

ET2 ES ET1 EX1 ET0 EX0

IE (Interrupt Enable) Register
Eg. Timer 1 interrupt is enabled as follow:
SETB ET1
SETB EA
or
MOV IE,#10001000B
Eg. External 0 and serial interrupts are enabled as follow:
SETB EX0
SETB ES
SETB EA
or
MOV IE,#10010001B
Ref. I. Scott Mackenzie
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Interrupt Priority
-

-

PT2 PS PT1 PX1 PT0 PX0

IP (Interrupt Priority) Register

•
•
•
•

•
•

PT2 : Priority for Timer 2 interrupt
PS: Priority for Serial port interrupt
PT1: Priority for Timer 1 interrupt
PX1: Priority for External 1 interrupt
PT0: Priority for Timer 0 interrupt
PX0: Priority for External 0 interrupt
1 = Higher Level; 0 = Lower Level

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Interrupt Priority
-

-

PT2 PS PT1 PX1 PT0 PX0

IP (Interrupt Priority) Register
• If 2 interrupts occur simultaneously

a high-priority ISR executes
• If a low-priority ISR is executing when a high-priority interrupts

the low-priority ISR is interrupted
 A high-priority interrupt can interrupt a low-priority ISR.
 A high-priority ISR cannot be interrupted.
• If 2 interrupts of the same priority occur simultaneously

a fixed polling sequence determines which is serviced first
 The polling sequence is external 0, Timer 0, external 1, Timer
1, serial port, Timer 2.
Ref. I. Scott Mackenzie

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Interrupt Flags
When an event occurs
the corresponding interrupt flag is set

Interrupt occurs

• 5 Interrupt Sources: 2 external interrupt, 2 timer interrupt
and 1 serial port interrupt
• 6 Interrupt Flags: IE0, IE1, TF0, TF1, TI, and RI

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Interrupt Flags
When an event occurs
the corresponding interrupt flag is set

Interrupt occurs
• When a falling edge occur at /INT0 pin
the IE0 flag is set

External 0 Interrupt occurs
• When a falling edge occur at /INT1 pin
the IE1 flag is set

External 1 Interrupt occurs
• When Timer 0 is overflow
the IE0 flag is set
Timer 0
Interrupt occurs
• When Timer 1 is overflow
the IE1 flag is set
Timer 1
Interrupt occurs
• When the transmission is done (transmit buffer is empty) or the
reception is done (receiver buffer is full)
the TI or RI flag is set

Serial Port Interrupt occurs.
Ref. I. Scott Mackenzie

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Interrupt Vectors
• When an interrupt is accepted, the value loaded into PC is
called interrupt vector. It is the address of the start of the
ISR.
INTERRUPT
System reset
External 0

FLAG
RST
IE0

Timer 0
External 1
Timer 1

TF0
IE1
TF1

000BH
0013H
001BH

Serial port
Timer 2

RI or TI
TF 2 or EXF2

0023H
002BH

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VECTOR ADDRESS
0000H
0003H

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Processing Interrupts
• When an interrupt (an event) occurs:
The corresponding interrupt flag is set
The current instruction completes execution.
The PC is saved on the stack.

The PC is loaded with the interrupt vector, which is the
address of the start of the ISR.
The interrupt flag is automatically cleared, except RI &TI (and
TF2 & EXF2 for 8052)
The ISR executes and takes action in response to the interrupt.
• The ISR finishes with a RETI (return from interrupt) instruction.
This retrieves the old value of the PC from the stack and
execution of the main program continues.
Ref. I. Scott Mackenzie

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An Example
• Assume that External 0 interrupt was enabled.
• When a falling edge (or level 0) is applied to pin P3.2 (/INT0)
IE0 is set
(automatically by hardware)
• The current PC is saved on the stack
• PC  0003H (and the main program is interrupted)
• The instruction at address 0003H (i.e. the first instruction of the ISR for
External 0) executes.
• When the ISR is done, the RETI instruction retrieves the old value of the PC
from the stack and the main program continues.
• Question: What will happen if there is NO falling edge (or level 0) applied to
pin P3.2 (/INT0) (i.e. NO interrupt signal occur) but bit IE0 is set by software
(i.e. by using SETB IE0)?
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External Interrupt
A push-button is connected to pin P3.2 (/INT0). A falling edge is created
when pushing this button. Write a program that sets pin P1.7 when pushing
the button down.

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External Interrupt
A push-button is connected to pin P3.2 (/INT0). A falling edge is created
when pushing this button. Write a program that sets pin P1.7 when pushing
the button down.
ORG 0000H
LJMP MAIN
ORG 0003H

;ISR External Int 0
SETB P1.7
RETI
ORG 0030H ;Main program
MAIN: SETB EA
SETB EX0 ;Enable Ext Int 0
SETB IT0 ;Falling edge
SJMP $
END

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Practice Problem 1
A push-button is connected to pin P3.2 (/INT0). A falling edge is created
when pushing this button. Write a program that creates one 10-ms pulse at
pin P1.7 when pushing the button down.

Ref. I. Scott Mackenzie

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Practice Problem 1
A push-button is connected to pin P3.2 (/INT0). A falling edge is created
when pushing this button. Write a program that creates one 10-ms pulse at
pin P1.7 when pushing the button down.

ORG 0000H
LJMP MAIN
ORG 0003H
SETB P1.7
ACALL DELAY10MS
CLR P1.7
RETI
ORG 0030H
MAIN:MOV TMOD,#01H
SETB EA
SETB EX0
Ref. I. Scott Mackenzie

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SETB IT0
SJMP $
DELAY10MS:
MOV TH0,#(-10000)

MOV TL0,#(-10000)
SETB TR0
JNB TF0,$
CLR TF0
CLR TR0
END
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Practice Problem 2
A push-button is connected to pin P3.3 (/INT1). A falling edge is created
when pushing this button. Write a program that increases the content of
location 40H of internal RAM when pushing the button down.

Ref. I. Scott Mackenzie

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Practice Problem 2
An push-button is connected to pin P3.3 (/INT1). A falling edge is created

when pushing this button. Write a program that increases the content of
location 40H of internal RAM.

ORG 0000H
LJMP MAIN
ORG 0013H ;Int vector of external int 1
INC 40H
RETI
ORG 0030H
MAIN:SETB EA
SETB EX1 ;Enable ext int 1
SETB IT1 ;Falling edge
SJMP $
END
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An Example of a Program Using Small ISR

ORG 0000H
LJMP MAIN
ORG 000BH
T0ISR:…
…
RETI
MAIN: …
…
END

;Reset
;Interrupt vector of Timer 0

;Return to main program

Ref. I. Scott Mackenzie

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An Example of a Program Using Large ISR
ORG 0000H
LJMP MAIN
ORG 0003H
LJMP E0ISR
ORG 000BH
LJMP T0ISR
ORG 0013H
LJMP E1ISR

ORG 001BH
LJMP T1ISR
ORG 0023H
LJMP SPISR
ORG 0030H
MAIN: …
SJMP $
E0ISR: …
RETI
T0ISR: …
RETI
… Mackenzie
Ref. I. Scott
END

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;Reset
;Interrupt vector of External 0
;Interrupt vector of Timer 0
;Interrupt vector of External 1
;Interrupt vector of Timer 1
;Interrupt vector of serial port

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Memory Organization

ISR Vector table

3-byte instruction

Ref. I. Scott Mackenzie

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Timer (8 bit) Interrupt
Write a program using Timer 0 and interrupt to create a 10 kHz square
wave on P1.0. (Crystal 12 MHz)
ORG 0000H
;Reset
LJMP MAIN
ORG 000BH
;Interrupt vector of Timer 0
T0ISR: CPL P1.0
RETI
ORG 0030H
MAIN: MOV TMOD,#02H
MOV TH0,#-50

SETB TR0
MOV IE,#82H
SJMP $
END

Ref. I. Scott Mackenzie

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Practice Problem 1
Write a program using Timer 1 and interrupt to create a 20 kHz square
wave on P1.7. (Crystal 24 MHz)

Ref. I. Scott Mackenzie

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Practice Problem 1
Write a program using Timer 1 and interrupt to create a 20 kHz square
wave on P1.7. (Crystal 24 MHz)
ORG 0000H
;Reset
LJMP MAIN
ORG 001BH
;Interrupt vector of Timer 1
T0ISR: CPL P1.7
RETI
ORG 0030H
MAIN: MOV TMOD,#20H
MOV TH1,#-50
SETB TR1
SETB EA
SETB ET1
SJMP $
END

Ref. I. Scott Mackenzie

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Practice Problem 2
Write a program using Timer 1 and interrupt to output data from A to
Port 1 every 100 us. Use crystal 12 MHz.

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Practice Problem 2
Write a program using Timer 1 and interrupt to output data from A to
Port 1 every 100 us. Use crystal 12 MHz.
ORG 0000H
LJMP MAIN
ORG 001BH
;Interrupt vector of Timer 1
MOV P1,A
RETI
ORG 0030H
MAIN: MOV TMOD,#20H
MOV TH1,#-100
SETB TR1
SETB EA
SETB ET1
SJMP $

END

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Practice Problem 3
Write a program using Timer and interrupt to send data from A to
serial port (UART 8 bit, 1200 baud) every 250 us. Use crystal 12 MHz.

Ref. I. Scott Mackenzie

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Practice Problem 3
Write a program using Timer and interrupt to send data from A to
serial port (UART 8 bit, 1200 baud) every 250 us. Use crystal 12 MHz.

ORG 0000H
LJMP MAIN
ORG 000BH
ACALL PHAT
RETI
ORG 0030H
MAIN: MOV TMOD,#22H
MOV SCON,#52H
MOV TH1,#-26
SETB TR1
MOV TH0,#-250
SETB TR0
SETB EA
SETB ET0
SJMP $
Ref. I. Scott Mackenzie

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PHAT:

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JNB TI,$
CLR TI
MOV SBUF,A
RET
END

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Timer (16 bit) Interrupt
Write a program using Timer 0 and interrupt to create a 1 kHz square
wave on P1.1. (Crystal 12 MHz)

Ref. I. Scott Mackenzie

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Timer (16 bit) Interrupt
Write a program using Timer 0 and interrupt to create a 1 kHz square
wave on P1.1. (Crystal 12 MHz)
ORG 0000H
LJMP CTCHINH
ORG 000BH
LJMP CTNGATTIMER0
ORG 0030H
CTCHINH:
MOV TMOD,#01H
MOV TH0,#HIGH(-500)
MOV TL0,#LOW(-500)

SETB TR0
SETB EA
SETB ET0
SJMP $

Ref. I. Scott Mackenzie

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CTNGATTIMER0:
CPL P1.1
CLR TR0
MOV TH0,#HIGH(-500)
MOV TL0,#LOW(-500)
SETB TR0
RETI
END

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Timer (16 bit) Interrupt

Write a program using Timer 0 and interrupt to create a 1 kHz square
wave on P1.1. (Crystal 12 MHz)
ORG 0000H
LJMP CTCHINH
ORG 000BH
LJMP CTNGATTIMER0
ORG 0030H
CTCHINH:
MOV TMOD,#01H
SETB EA
SETB ET0
SETB TF0 ; Ép ngắt
SJMP $

Ref. I. Scott Mackenzie

CTNGATTIMER0:
CPL P1.1
CLR TR0
MOV TH0,#HIGH(-500)
MOV TL0,#LOW(-500)
SETB TR0
RETI
END

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Practice Problem 1

Write a program using Timer 1 and interrupt to create a 100 Hz
square wave on P1.2. (Crystal 24MHz)

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Practice Problem 1
Write a program using Timer 1 and interrupt to create a 100 Hz
square wave on P1.2. (Crystal 24MHz)
ORG 0000H
LJMP CTCHINH
ORG 001BH
LJMP CTNGATTIMER1
ORG 0030H
CTCHINH:
MOV TMOD,#10H
SETB EA
SETB ET1

SETB TF1 ; Ép ngắt
SJMP $

Ref. I. Scott Mackenzie

CTNGATTIMER1:
CPL P1.2
CLR TR1
MOV TH1,#HIGH(-10000)
MOV TL1,#LOW(-10000)
SETB TR1
RETI
END

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Practice Problem 2
Write a program using Timer 1 and interrupt to complement P1.2
every 1 sec. (Crystal 12 MHz)

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Practice Problem 2
Write a program using Timer 1 and interrupt to complement P1.2
every 1 sec. (Crystal 12 MHz)
ORG 0000H
LJMP CTCHINH
ORG 001BH
LJMP CTNGATTIMER1
ORG 0030H
CTCHINH:
MOV TMOD,#10H
SETB EA
SETB ET1
SETB TF1 ; Ép ngắt
SJMP $

Ref. I. Scott Mackenzie

CTNGATTIMER1:
CPL P1.2
CLR TR1
MOV TH1,#HIGH(-10000)
MOV TL1,#LOW(-10000)
SETB TR1

RETI
END

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Two Square Waves Using Timer Interrupts
Write a program using interrupts to create 7 kHz and 500 Hz square
waves on P1.7 and P1.6. (Crystal 12 MHz)

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Two Square Waves Using Timer Interrupts
Write a program using interrupts to create 7 kHz and 500 Hz square
waves on P1.7 and P1.6
ORG 0000H

LJMP MAIN
ORG 000BH
LJMP T0ISR
ORG 001BH
LJMP T1ISR
ORG 0030H
MAIN: MOV TMOD,#12H
MOV IE,#8AH
MOV TH0,#-71
SETB TR0
MOV TH1,#HIGH(-1000)
MOV TL1,#LOW(-1000)
SETB TR1
SJMP $

Ref. I. Scott Mackenzie

T0ISR: CPL P1.7
RETI
T1ISR: CPL P1.6
CLR TR1
MOV TH1,#HIGH(-1000)
MOV TL1,#LOW(-1000)
SETB TR1
RETI
END

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Character Output Using Interrupts
Write a program using interrupts to continually transmit the ASCII code set
(excluding control codes) to a terminal attached to the 8051’s serial port (1200
baud, 12 MHz crystal). The ASCII codes consist of 95 graphic codes (20H to 7EH) and
33 control codes (00H to 1FH, and 7FH).
ORG 0000H
LJMP MAIN
ORG 0023H
LJMP SPISR
ORG 0030H
MAIN: MOV TMOD,#20H
MOV TH1,#-26
SETB TR1
MOV SCON,#42H
MOV IE,#90H
MOV A,#20H
SETB TI
SJMP $

Ref. I. Scott Mackenzie

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SPISR: CJNE A,#7FH,SKIP
MOV A,#20H
SKIP: MOV SBUF,A
INC A
CLR TI
RETI

END

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Character Output Using Interrupts (2)
Write a program using interrupts to continually transmit the ASCII code set
(excluding control codes) to a terminal attached to the 8051’s serial port (1200
baud, 12 MHz crystal). The ASCII codes consist of 95 graphic codes (20H to 7EH) and
33 control codes (00H to 1FH, and 7FH).

Ref. I. Scott Mackenzie

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Character Output Using Interrupts (2)
Write a program using interrupts to continually transmit the ASCII code set
(excluding control codes) to a terminal attached to the 8051’s serial port (1200
baud, 12 MHz crystal). The ASCII codes consist of 95 graphic codes (20H to 7EH) and
33 control codes (00H to 1FH, and 7FH).

ORG 0000H
LJMP MAIN
ORG 0023H
LJMP SPISR
ORG 0030H
MAIN: MOV SCON,#52H
MOV TMOD,#20H
MOV TH1,#-26
SETB TR1
MOV A,#20H
MOV IE,#90H
SJMP $

Ref. I. Scott Mackenzie

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SPISR: CLR TI
MOV SBUF,A
INC A
CJNE A,#7FH,SKIP
MOV A,#20H
SKIP: RETI
END

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Furnace Controller
Using interrupts, design an 8051 furnace controller that keeps a building at 20oC ± 1oC.
Temperature sensors are connected to /INT0 and /INT1 and provide /HOT and /COLD
signals. The furnace ON/OFF solenoid is connected to P1.7.
/HOT = 0 if T > 21oC
/COLD = 0 if T < 19oC
P1.7 = 1 : Furnace ON
P1.7 = 0 : Furnace OFF

Ref. I. Scott Mackenzie

P3.2

P3.3

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Furnace Controller
Using interrupts, design an 8051 furnace controller that keeps a building at 20oC ± 1oC.

E0ISR:

E1ISR:

MAIN:

SKIP:

ORG 0000H
LJMP MAIN
ORG 0003H
CLR P1.7
RETI
ORG 0013H
SETB P1.7
RETI
ORG 0030H
MOV IE,#85H
SETB IT0
SETB IT1
SETB P1.7
JB P3.2,SKIP
CLR P1.7
SJMP $
END

Ref. I. Scott Mackenzie

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;turn furnace off

;turn furnace on

;enable external 0 & 1 interrupts
;negative edge triggered for external 0
;negative edge triggered for external 1
;turn furnace on
;if T > 21 degrees,
; turn furnace off
;do nothing

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Intrusion Warning System (1)
Design an intrusion warning system using interrupts that sounds a 400 Hz tone using
loudspeaker connected to P1.7 whenever a door sensor connected /INT0 makes a
high-to-low transition.

P3.2

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Intrusion Warning System (1)
Design an intrusion warning system using interrupts that sounds a 400 Hz tone using
loudspeaker connected to P1.7 whenever a door sensor connected /INT0 makes a
high-to-low transition.
ORG 0000H
LJMP MAIN
ORG 0003H
LJMP E0ISR
ORG 001BH
LJMP T1ISR
ORG 0030H
MAIN: SETB IT0
MOV TMOD,#10H
MOV IE,#81H
SJMP $
E0ISR: SETB TF1
SETB ET1
RETI

Ref. I. Scott Mackenzie

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T1ISR: CLR TR1
MOV TH1,#HIGH(-1250)
MOV TL1,#LOW(-1250)

CPL P1.7
SETB TR1
RETI
END

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Intrusion Warning System (2)
Design an intrusion warning system using interrupts that sounds a 400 Hz tone for
50 ms (using loudspeaker connected to P1.7) whenever a door sensor connected
/INT0 makes a high-to-low transition.

P3.2

50 ms

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Intrusion Warning System (2)
Design an intrusion warning system using interrupts that sounds a 400 Hz tone for
50 ms (using loudspeaker connected to P1.7) whenever a door sensor connected
/INT0 makes a high-to-low transition.
ORG 0000H
LJMP MAIN
ORG 0003H
LJMP E0ISR
ORG 000BH
LJMP T0ISR
ORG 001BH
LJMP T1ISR
ORG 0030H
MAIN: SETB IT0
MOV TMOD,#11H
MOV IE,#81H
SJMP $
E0ISR: MOV TH0,#HIGH(-50000)
MOV TL0,#LOW(-50000)
SETB TR0
SETB
TF1
Ref. I. Scott
Mackenzie

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SETB ET0
SETB ET1

RETI
T0ISR: CLR TR0
CLR ET0
CLR ET1
RETI
T1ISR: CLR TR1
MOV TH1,#HIGH(-1250)
MOV TL1,#LOW(-1250)
CPL P1.7
SETB TR1
RETI
END

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