1. registers used in timer/counter th0, tl0, th1, tl1 tmod (timer mode register) tcon (timer...

Registers Used in Timer/CounterRegisters Used in Timer/Counter

TH0, TL0, TH1, TL1 TH0, TL0, TH1, TL1 TMOD (Timer mode register)TMOD (Timer mode register) TCON (Timer control register)TCON (Timer control register)

22

Timer registerTimer register

D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0

TH0 /TH1 TL0/TL1

33

TMOD RegisterTMOD Register::

Gate : When set, timer only runs while INT(0,1) is high.

C/T : Counter/Timer select bit.

M1 : Mode bit 1. M0 : Mode bit 0.

44

TCON Register:TCON Register:

TF1: Timer 1 overflow flag. TR1: Timer 1 run control bit. TF0: Timer 0 overflag. TR0: Timer 0 run control bit. IE1: External interrupt 1 edge flag. IT1: External interrupt 1 type flag. IE0: External interrupt 0 edge flag. IT0: External interrupt 0 type flag.

55

Timer modesTimer modes

Timer Mode 0 Timer Mode 0 :: Emulates 8048 counter/timer (13-bits).Emulates 8048 counter/timer (13-bits). 8-bit counter (TL0 or TL1).8-bit counter (TL0 or TL1). 5-bit prescaler (TH0 or TH1).5-bit prescaler (TH0 or TH1).

66

Timer Mode 1 Timer Mode 1 :: Simple 16-bit counter.Simple 16-bit counter. -Timer Mode 2 :-Timer Mode 2 : 8-bit auto-reload.8-bit auto-reload. Counter in TL0 or TL1.Counter in TL0 or TL1. Reload value in TH0 or TH1.Reload value in TH0 or TH1. Provides a periodic flag or interruptProvides a periodic flag or interrupt

77

Timer Mode 3 Timer Mode 3

Splits timer 0 into two 8-bit counter/timers.Splits timer 0 into two 8-bit counter/timers. First counter (TLO) acts like mode 0,First counter (TLO) acts like mode 0,

without prescaler.without prescaler. Second counter (TH0):Second counter (TH0): Counts CPU cycles.Counts CPU cycles. Uses TR1 (timer 1 run bit) as enable.Uses TR1 (timer 1 run bit) as enable. Uses TF1 (timer 1 overflow bit) as flag.Uses TF1 (timer 1 overflow bit) as flag. Uses Timer 1 interrupt.Uses Timer 1 interrupt.

88

TIMING MODE DIAGRAMTIMING MODE DIAGRAM

99

ANIMATED TIMER MODE:ANIMATED TIMER MODE:

TMOD TH1 TL1

FF

FB

TR1

FFFB FFFC FFFD FFFE FFFFFFFF+01

1 00 1

SFR

TF1

1010

ANIMATED TIMER MODE:ANIMATED TIMER MODE:

TMOD TH1 TL1

FF

FB

TR1

FFFB FFFC FFFD FFFE FFFFFFFF+01

1 00 1

SFR

TF1

1111

SAMPLE PGM FOR TIMER:SAMPLE PGM FOR TIMER:

ORG 0HORG 0H START:SETB P1.0START:SETB P1.0 ACALL DELAYACALL DELAY CLR P1.0CLR P1.0 ACALL DELAYACALL DELAY SJMP STARTSJMP START

1313

SAMPLE PROGRAMSAMPLE PROGRAM

DELAY:MOV TMOD,#0001 0000B ;10HDELAY:MOV TMOD,#0001 0000B ;10H

MOV TL1,#00MOV TL1,#00

MOV TH1,#00MOV TH1,#00

SETB TR1SETB TR1

JNB TF1,LOOPJNB TF1,LOOP

CLR TR1CLR TR1

CLR TF1 CLR TF1

RETRET1414

SCON REGISTERSCON REGISTER

1616

SM0,SM1SM0,SM1

- SM0, SM1 = Serial Mode:- SM0, SM1 = Serial Mode: 00 = Mode 0 : Shift register I/O expansion.00 = Mode 0 : Shift register I/O expansion. 01 = Mode 1 : 8-bit UART with variable baud 01 = Mode 1 : 8-bit UART with variable baud

rate.rate. 10 = Mode 2 : 9-bit UART with fixed baud 10 = Mode 2 : 9-bit UART with fixed baud

rate.rate. 11 = Mode 3 : 9-bit UART with variable baud 11 = Mode 3 : 9-bit UART with variable baud

rate.rate.

1717

SM2SM2

- SM2 :- SM2 : Mode 0 : Not used.Mode 0 : Not used. Mode 1 : 1 = Ignore bytes with no stop bit.Mode 1 : 1 = Ignore bytes with no stop bit. Mode 2,3 : 0 = Set receive interrupt (RI) on Mode 2,3 : 0 = Set receive interrupt (RI) on

all bytes.all bytes. : 1 = Set RI on bytes where bit 9 = 1.: 1 = Set RI on bytes where bit 9 = 1.

1818

REN = Enables receiver.REN = Enables receiver. - TB8 = Ninth bit transmitted (in modes 2 - TB8 = Ninth bit transmitted (in modes 2

and 3).and 3). - RB8 = Ninth bit received:- RB8 = Ninth bit received: Mode 0 : Not used.Mode 0 : Not used. Mode 1 : Stop bit.Mode 1 : Stop bit. Mode 2,3 : Ninth data bit.Mode 2,3 : Ninth data bit. - TI = Transmit interrupt flag.- TI = Transmit interrupt flag. - RI = Receive interrupt flag.- RI = Receive interrupt flag.

1919

BAUD RATEBAUD RATE

TH1(DECIMAL) TH1(HEX) SMOD=0 SMOD=1

-3 FD 9,600 19,200

-6 FA 4,800 9,600

-12 F4 2,400 4,800

-24 F8 1,200 2,400

2121

Mode 1:TXMode 1:TX

2424

MODE 1:TXMODE 1:TX

8 BIT DATASBUF

DATA

8

BIT DATA

STOP BIT

START BIT

PARALLEL TO SERIAL TX

SERIAL DATA TRANSFER

STARTSTOP

TI = 0TI=1

2525

MODE 1:TXMODE 1:TX

8 BIT DATASBUF

DATA

8

BIT DATA

STOP BIT

START BIT



STARTSTOP

TI = 0TI=1

2626

DATA TX SERIALLY:DATA TX SERIALLY:

Load TMOD RegisterLoad TMOD Register ;;timer1timer1 Load TH1 or TL1 values ; for Load TH1 or TL1 values ; for Baud rateBaud rate Load SCON register; Load SCON register; serial mode 0,1,2,3serial mode 0,1,2,3 SET TR1 ;SET TR1 ;To start the timerTo start the timer Character byte is written to SBUF;Character byte is written to SBUF; Check if TI=1;Check if TI=1; CLR TICLR TI Reload the value again.Reload the value again.

2727

SAMPLE PROGRAM:TXSAMPLE PROGRAM:TX MOV TMOD,#20HMOV TMOD,#20H MOV TH1,#-3MOV TH1,#-3 MOV SCON,#50HMOV SCON,#50H SETB TR1SETB TR1 AGAIN:MOV SBUF,#’Y’AGAIN:MOV SBUF,#’Y’ JNB TI ,HereJNB TI ,Here CLR TICLR TI SJMP AGAINSJMP AGAIN

2828

SERIAL DATA TRANSFERSERIAL DATA TRANSFER

DISPLAY

Y

N

8051

2929

SAMPLE PROGRAM:SAMPLE PROGRAM: MOV TMOD,#20HMOV TMOD,#20H MOV TH1,#-3MOV TH1,#-3 MOV SCON,#50HMOV SCON,#50H SETB TR1SETB TR1 AGAIN:MOV SBUF,#’Y’AGAIN:MOV SBUF,#’Y’ JNB TI,HereJNB TI,Here CLR TICLR TI MOV P1,#’N’MOV P1,#’N’ SJMP AGAINSJMP AGAIN

3030

Mode 1:RXMode 1:RX

3131

MODE 1:RXMODE 1:RX

SBUF

8

BIT DATA

STOP BIT

START BIT


SERIAL DATA RECEIVE

STOPSTART

8 BIT DATA

DATA RX

RI=0RI=1

3232

SAMPLE PROGRAM:RXSAMPLE PROGRAM:RX

Load Load TMODTMOD Value. Value. Load TH1 value ;baud rateLoad TH1 value ;baud rate Load SCON RegisterLoad SCON Register Set TR1 To start timer.Set TR1 To start timer. Clear RIClear RI Check the RI each time.Check the RI each time. When RI =1,Load the value from SBUF.When RI =1,Load the value from SBUF.

3333

SAMPLE PROGRAM:RXSAMPLE PROGRAM:RX

MOV TMOD,#20HMOV TMOD,#20H MOV TH1,#-3MOV TH1,#-3 MOV SCON,#50HMOV SCON,#50H SETB TR1SETB TR1 CLR RICLR RI LOOP:JNB RI,LOOPLOOP:JNB RI,LOOP MOV A,SBUFMOV A,SBUF ENDEND

3434

SERIAL PORT TRANSMITTERSERIAL PORT TRANSMITTER

3535

SERIAL MODE 2SERIAL MODE 2

8 BIT DATASBUF

DATA

8

BIT DATA

STOP BIT

START BIT



STARTSTOP

TI = 0TI=1

TB8=0 TB8=1

3636

RECEIVE DATARECEIVE DATA

3737

SERIAL MODE 2 :RXSERIAL MODE 2 :RX

SBUF

8

BIT DATA

STOP BIT

START BIT


SERIAL DATA RECEIVE

STOPSTART

8 BIT DATA

DATA RX

RI=0RI=1

RB8=0

3838

Interrupt :Interrupt :

3939

Interrupts ProgrammingInterrupts Programming

An An interruptinterrupt is an external or internal event that is an external or internal event that interrupts the microcontroller to inform it that a device interrupts the microcontroller to inform it that a device needs its service.needs its service.

Interrupts vs. PollingInterrupts vs. Polling A single microcontroller can serve A single microcontroller can serve severalseveral devices. devices. ThThereere are are twotwo ways to do that: ways to do that:

– interrupts interrupts – polling.polling.

The program which is associated with the interrupt is The program which is associated with the interrupt is called the called the interrupt service routineinterrupt service routine (ISR) or (ISR) or interrupt interrupt handlerhandler..

4040

Steps in executing an interruptSteps in executing an interrupt FFinishinish current current instruction and s instruction and saaves the PC on stack.ves the PC on stack.

JJumps to a fixed location in memory umps to a fixed location in memory depend on type of depend on type of interruptinterrupt

SStarts to execute the interrupt service routine until RETI tarts to execute the interrupt service routine until RETI (return from interrupt)(return from interrupt)

Upon executing the RETI the microcontroller returns to Upon executing the RETI the microcontroller returns to the place where it was interrupted. Getthe place where it was interrupted. Get poppop PC from PC from stack stack

4141

PROGRAM COUNTERPROGRAM COUNTER

It saves the address next insturction going It saves the address next insturction going to be executed.to be executed.

4242

MAIN PGM

ISRINTERRUPTPROGRAM

END

4343

ExampleExample A 10khz square wave with 50% duty cycleA 10khz square wave with 50% duty cycle

ORG ORG 00 ;Reset entry poit;Reset entry poit

LJMPLJMP MAINMAIN ;Jump above interrupt;Jump above interrupt

ORGORG 000BH000BH ;Timer 0 interrupt vector;Timer 0 interrupt vector

T0ISR:CPLT0ISR:CPL P1.0P1.0 ;Toggle port bit;Toggle port bit

RETIRETI ;Return from ISR to Main program;Return from ISR to Main program

ORG 0030HORG 0030H ;Main Program entry point;Main Program entry point

0030:MAIN:0030:MAIN: MOVMOV TMOD,#02HTMOD,#02H ;Timer 0, mode 2;Timer 0, mode 2

0032:0032: MOVMOV TH0,#-50TH0,#-50 ;50 us delay;50 us delay

0034:0034: SETBSETB TR0TR0 ;Start timer;Start timer

0036:0036: MOVMOV IE,#82HIE,#82H ;Enable timer 0 interrupt;Enable timer 0 interrupt

0038:0038: SJMPSJMP $$ ;Do nothing just wait;Do nothing just wait

ENDEND

A 10khz square wave with 50% duty cycleA 10khz square wave with 50% duty cycle

ORG ORG 00 ;Reset entry poit;Reset entry poit

LJMPLJMP MAINMAIN ;Jump above interrupt;Jump above interrupt

ORGORG 000BH000BH ;Timer 0 interrupt vector;Timer 0 interrupt vector

T0ISR:CPLT0ISR:CPL P1.0P1.0 ;Toggle port bit;Toggle port bit

RETIRETI ;Return from ISR to Main program;Return from ISR to Main program

ORG 0030HORG 0030H ;Main Program entry point;Main Program entry point

0030:MAIN:0030:MAIN: MOVMOV TMOD,#02HTMOD,#02H ;Timer 0, mode 2;Timer 0, mode 2

0032:0032: MOVMOV TH0,#-50TH0,#-50 ;50 us delay;50 us delay

0034:0034: SETBSETB TR0TR0 ;Start timer;Start timer

0036:0036: MOVMOV IE,#82HIE,#82H ;Enable timer 0 interrupt;Enable timer 0 interrupt

0038:0038: SJMPSJMP $$ ;Do nothing just wait;Do nothing just wait

ENDEND4444

INTERRUPT PGMINTERRUPT PGM

MAIN PGM

ISR

STACK POINTER

0B

0A

09

08 PCL

PCH

INTERRUPT

38

00

4545

Interrupt SourcesInterrupt Sources

Original 8051 has 6 sources of interruptsOriginal 8051 has 6 sources of interrupts– Reset Reset – Timer 0 overflowTimer 0 overflow– Timer 1 overflowTimer 1 overflow– External Interrupt 0External Interrupt 0– External Interrupt 1External Interrupt 1– Serial Port events (buffer full, buffer empty, etc)Serial Port events (buffer full, buffer empty, etc)

Enhanced version has 22 sourcesEnhanced version has 22 sources– More timers, programmable counter array, ADC, more external More timers, programmable counter array, ADC, more external

interrupts, another serial port (UART)interrupts, another serial port (UART)

4646

Interrupt VectorsInterrupt Vectors

Each interrupt has a Each interrupt has a specificspecific place in place in codecode memory where memory where program execution (interrupt service routine) begins.program execution (interrupt service routine) begins.

External Interrupt 0: External Interrupt 0: 0003h0003h

Timer 0 overflow: Timer 0 overflow: 000Bh000Bh

External Interrupt 1:External Interrupt 1: 0013h0013h

Timer 1 overflow: Timer 1 overflow: 001Bh001Bh

Serial : 0023hSerial : 0023h

Timer 2 overflowTimer 2 overflow(8052+)(8052+) 002bh 002bh

Note: that there are only 8 memory locations between vectors.

4747

SJMPSJMP main main ORGORG 03H03H

ljmpljmp int0srint0srORGORG 0BH0BHljmpljmp t0srt0srORGORG 13H13Hljmpljmp int1srint1srORGORG 1BH1BHljmpljmp t1srt1srORGORG 23H23Hljmpljmp serialsrserialsrORGORG 30H30H

main:main: ……

ENDEND

ISRs and Main Program in 8051

4848

Interrupt Enable Register :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..

4949

Enabling and disabling an interrupt

by bit operationRecommended in the middle of program

SETB EA ;Enable All SETB ET0 ;Enable Timer0 ovrf SETB ET1 ;Enable Timer1 ovrfSETB EX0 ;Enable INT0SETB EX1 ;Enable INT1SETB ES ;Enable Serial port

by mov instructionRecommended in the first of program

MOV IE, #10010110B

SETB IE.7SETB IE.1SETB IE.3SETB IE.0SETB IE.2 SETB IE.4

5050

Timer ISRTimer ISR

Notice thatNotice that– There is no need for a “CLR TFx” instruction in There is no need for a “CLR TFx” instruction in

timer ISR timer ISR – 8051 clears the TF internally upon jumping to 8051 clears the TF internally upon jumping to

ISRISR

Notice that Notice that – We must reload timer in mode 1We must reload timer in mode 1– There is no need on mode 2 (timer auto reload)There is no need on mode 2 (timer auto reload)

5151

External interrupt type controlExternal interrupt type control By low nibble of Timer control register By low nibble of Timer control register TCONTCON

IE0IE0 ( (IE1IE1): External interrupt 0(1) edge flag. ): External interrupt 0(1) edge flag.

– setset by CPU when external interrupt edge ( by CPU when external interrupt edge (H-to-LH-to-L) is detected. ) is detected.

– Does not affected by H-to-L while ISR is executed(no int on int)Does not affected by H-to-L while ISR is executed(no int on int)

– ClearCleared by CPU when ed by CPU when RETIRETI executed. executed.

– does does not not latch low-levellatch low-level triggered interrupt triggered interrupt

IT0IT0 ((IT1IT1): interrupt 0 (1) type control bit. ): interrupt 0 (1) type control bit.

– Set/cleared by softwareSet/cleared by software

– IT=1 edge trigger IT=1 edge trigger

– IT=0 low-level triggerIT=0 low-level trigger

TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0Timer 1 Timer0 for Interrupt

(MSB) (LSB)

5252

External Interrupts

IE0 (TCON.3)

0003

INT0(Pin 3.2) 0

12

IT0

Edge-triggered

Level-triggered (default)

IE1 (TCON.3)

INT0(Pin 3.3) 0

12

IT1

Edge-triggered

Level-triggered (default)

0013

5353

Interrupt PrioritiesInterrupt Priorities What if What if twotwo interrupt sources interrupt at the interrupt sources interrupt at the same same

timetime??

The interrupt with the The interrupt with the highesthighest PRIORITY gets serviced PRIORITY gets serviced firstfirst..

All interrupts have a power on All interrupts have a power on defaultdefault priority order. priority order.

1.1. External interrupt 0 (INT0)External interrupt 0 (INT0)

2.2. Timer interrupt0 (TF0)Timer interrupt0 (TF0)

3.3. External interrupt 1 (INT1)External interrupt 1 (INT1)

4.4. Timer interrupt1 (TF1)Timer interrupt1 (TF1)

5.5. Serial communication (RI+TI)Serial communication (RI+TI)

Priority can also be set to “high” or “low” by Priority can also be set to “high” or “low” by IPIP reg. reg.

5454

Interrupt Priorities (IP) RegisterInterrupt Priorities (IP) Register

IP.7IP.7: reserved: reserved

IP.6IP.6: reserved: reserved

IP.5IP.5: timer 2 interrupt priority bit(8052 only): timer 2 interrupt priority bit(8052 only)

IP.4IP.4: serial port interrupt priority bit: serial port interrupt priority bit

IP.3IP.3: timer 1 interrupt priority bit: timer 1 interrupt priority bit

IP.2IP.2: external interrupt 1 priority bit: external interrupt 1 priority bit

IP.1IP.1: timer 0 interrupt priority bit: timer 0 interrupt priority bit

IP.0IP.0: external interrupt 0 priority bit: external interrupt 0 priority bit

--- PX0PT0PX1PT1PSPT2---

5555

Interrupt Priorities ExampleInterrupt Priorities Example

MOV IP , #00000100BMOV IP , #00000100B or or SETB IP.2SETB IP.2 gives priority order gives priority order1.1. Int1Int1

2.2. Int0Int0

3.3. Timer0Timer0

4.4. Timer1Timer1

5.5. SerialSerial

MOV IP , #00001100BMOV IP , #00001100B gives priority order gives priority order1.1. Int1Int1

2.2. Timer1Timer1

3.3. Int0Int0

4.4. Timer0Timer0

5.5. SerialSerial


5656

Interrupt inside an interruptInterrupt inside an interrupt


A high-priority interrupt can interrupt a low-priority interrupy

All interrupt are latched internally

Low-priority interrupt wait until 8051 has finished servicing the high-priority interrupt

5757

Example of external interuuptExample of external interuuptORG 0000HORG 0000HLJMP MAINLJMP MAIN

;;

;interrupt service routine (ISR) ;interrupt service routine (ISR) ;for hardware external interrupt INT1;for hardware external interrupt INT1;;

ORG 0013HORG 0013HSETB P1.1SETB P1.1MOV R0,200MOV R0,200

WAIT:WAIT: DJNZ R0,WAITDJNZ R0,WAITCLR P1.1CLR P1.1RETIRETI

;;

;main program for initialization;main program for initialization;;

ORG 30HORG 30HMAIN:MAIN: SETB IT1SETB IT1 ;on negative edge of INT1;on negative edge of INT1

MOV IE,#10000100BMOV IE,#10000100BWAIT2:WAIT2: SJMP WAIT2SJMP WAIT2

ENDEND

5858

1. registers used in timer/counter th0, tl0, th1, tl1 tmod (timer mode register) tcon (timer...

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