Microcontroller 8051 timer and counter module

Microcontroller 8051 timer and counter module

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  1 8051 Timer Programmingin Assembly and C Prepared By: 1400731090010 140073109012 140073109013
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  2 Inside Architecture of8051 CPU On-chip RAM On-chip ROM for program code 4 I/O Ports Timer 0 Serial Port Figure 1-2. Inside the 8051 Microcontroller Block Diagram OSC Interrupt Control External interrupts Timer 1 Timer/Counter Bus Control TxD RxD P0 P1 P2 P3 Address/Data Counter Inputs
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  3 Timers /Counters • The8051 has 2 timers/counters: timer/counter 0 and timer/counter 1. They can be used as 1. The timer is used as a time delay generator. – The clock source is the internal crystal frequency of the 8051. 2. An event counter. – External input from input pin to count the number of events on registers. – These clock pulses cold represent the number of people passing through an entrance, or the number of wheel rotations, or any other event that can be converted to pulses.
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  4 Timer • 8051 timersuse 1/12 of XTAL frequency as the input of timers, regardless of machine cycle. • Because the input of timer is a regular, fixed- periodic square wave, we can count the number of pulses and calculate the time delay. to LCD P1 8051 TL0 TH0 Set Timer 0 XTAL oscillator ÷ 12 Timer
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  5 Counter • Count thenumber of events • External input from Tx input pin (x=0 or 1). • We use Tx to denote T0 or T1. – External input from T0 input pin (P3.4) for Counter 0 – External input from T1 input pin (P3.5) for Counter 1 T0 to LCD P3.4 P1 8051 a switch TL0 TH0 Vcc
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  6 Figure 9-8: Timer/Counter0 XTAL oscillator ÷ 12 TR0 INT0 Pin Pin 3.2 C/T = 0 Gate T0 Pin Pin 3.4 C/T = 1 TH0 TL0 TF0 1. monitor by JNB 2. interrupt timer input hardware control 1:start 0:stop counter input Sec 9.2 
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  7 Figure 9-9: Timer/Counter1 XTAL oscillator ÷ 12 TR1 INT1 Pin Pin 3.3 C/T = 0 Gate T1 Pin Pin 3.5 C/T = 1 TH1 TL1 TF1 1. monitor by JNB 2. interrupt 1:start 0:stop timer input counter input hardware control
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  8 Registers Used inTimer/Counter • TH0, TL0 (Timer 0 registers) • TH1, TL1 (Timer 1 registers) • TMOD (Timer mode register) • TCON (Timer control register) • You can see Appendix H (pages 607-611) for details. • Since 8052 has 3 timers/counters, the formats of these control registers are different. – T2CON (Timer 2 control register), TH2 and TL2 used for 8052 only.
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  9 Basic Registers ofthe Timer • Both Timer 0 and Timer 1 are 16 bits wide. – Each 16-bit timer can be accessed as two separate registers of low byte and high byte. – Timer 0: TH0 & TL0 • Timer 0 high byte, timer 0 low byte – Timer 1: TH1 & TL1 • Timer 1 high byte, timer 1 low byte – These registers stores • the time delay as a timer • the number of events as a counter
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  10 Timer Registers D15 D8 D9 D10 D11 D12 D13 D14D7 D0 D1 D2 D3 D4 D5 D6 TH0 TL0 D15 D8 D9 D10 D11 D12 D13 D14 D7 D0 D1 D2 D3 D4 D5 D6 TH1 TL1 Timer 0 Timer 1
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  11 TCON Register (1/2) •Timer control register: TCON – Upper nibble for timer/counter, lower nibble for interrupts • TR (run control bit) – TR0 for Timer/counter 0; TR1 for Timer/counter 1. – TRx is set by programmer to turn timer/counter on/off. • TRx=0: off (stop) • TRx=1: on (start) TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0 Timer 1 Timer0 for Interrupt (MSB) (LSB)
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  12 TCON Register (2/2) •TF (timer flag, control flag) – TF0 for timer/counter 0; TF1 for timer/counter 1. – TFx is like a carry. Originally, TFx=0. When TH-TL roll over to 0000 from FFFFH, the TFx is set to 1. • TFx=0 : not reach • TFx=1: reach • If we enable interrupt, TFx=1 will trigger ISR. TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0 Timer 1 Timer0 for Interrupt (MSB) (LSB)
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  13 Table 9-2: EquivalentInstructions for the Timer Control Register For timer 0 SETB TR0 = SETB TCON.4 CLR TR0 = CLR TCON.4 SETB TF0 = SETB TCON.5 CLR TF0 = CLR TCON.5 For timer 1 SETB TR1 = SETB TCON.6 CLR TR1 = CLR TCON.6 SETB TF1 = SETB TCON.7 CLR TF1 = CLR TCON.7 TF1 IT0 IE0 IT1 IE1 TR0 TF0 TR1 TCON: Timer/Counter Control Register
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  14 TMOD Register • Timermode register: TMOD MOV TMOD,#21H – An 8-bit register – Set the usage mode for two timers • Set lower 4 bits for Timer 0 (Set to 0000 if not used) • Set upper 4 bits for Timer 1 (Set to 0000 if not used) – Not bit-addressable GATE C/T M1 M0 GATE C/T M1 M0 Timer 1 Timer 0 (MSB) (LSB)
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  15 Figure 9-3. TMODRegister GATE Gating control when set. Timer/counter is enabled only while the INTx pin is high and the TRx control pin is set. When cleared, the timer is enabled whenever the TRx control bit is set. C/T Timer or counter selected cleared for timer operation (input from internal system clock). Set for counter operation (input from Tx input pin). M1 Mode bit 1 M0 Mode bit 0 GATE C/T M1 M0 GATE C/T M1 M0 Timer 1 Timer 0 (MSB) (LSB)
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  16 C/T (Clock/Timer) • Thisbit is used to decide whether the timer is used as a delay generator or an event counter. • C/T = 0 : timer • C/T = 1 : counter
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  17 Gate • Every timerhas a mean of starting and stopping. – GATE=0 • Internal control • The start and stop of the timer are controlled by software. • Set/clear the TR0 (or TR1) for start/stop timer. – GATE=1 • External control • The hardware way of starting and stopping the timer by software and an external source. • Timer/counter is enabled only while the INT0 (or INT1) pin has an 1 to 0 transition and the TR0 (or TR1) control pin is set. • INT0: P3.2, pin 12; INT1: P3.3, pin 13.
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  18 M1, M0 • M0and M1 select the timer mode for timers 0 & 1. M1 M0 Mode Operating Mode 0 0 0 13-bit timer mode 8-bit THx + 5-bit TLx (x= 0 or 1) 0 1 1 16-bit timer mode 8-bit THx + 8-bit TLx (x= 0 or 1) 1 0 2 8-bit auto reload 8-bit auto reload timer/counter; THx holds a value which is to be reloaded into TLx each time it overflows. 1 1 3 Split timer mode
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