Special Function Register Map

Transcription

1 Bit Addressable Special Function Register Map F8 F0 B E8 E0 ACC D8 D0 PSW C8 C0 B8 IP B0 P3 A8 IE A0 P2 98 SCON SBUF 90 P1 88 TCON TMOD TL0 TL1 TH0 TH1 80 P0 SP DPH DPL PCON 8051 MICROCONTROLLER TIMERS 0 & 1 1

2 Special Function Registers Interrupt control: IE IP : Interrupt Enable. : Interrupt Priority. TImers: TMOD TCON TH0 TL0 TH1 TL1 : Timer mode. : Timer control. : Timer 0 high byte. : Timer 0 low byte. : Timer 1 high byte. : Timer 1 low byte MICROCONTROLLER TIMERS 0 & 1 2

3 Counter / Timers Two 16-bit Counter/Timers: TIMER0, TIMER1 Up counters, can interrupt on overflow. Counts: - CPU cycles (crystal/12). Timer. - External input (max. half CPU rate). Counter. Four Operation Modes MICROCONTROLLER TIMERS 0 & 1 3

4 Timer Modes - Timer Mode 0 : Emulates 8048 counter/timer (13-bits). 8-bit counter (TL0 or TL1). 5-bit prescaler (TH0 or TH1). - Timer Mode 1 : Simple 16-bit counter. - Timer Mode 2 : 8-bit auto-reload. Counter in TL0 or TL1. Reload value in TH0 or TH1. Provides a periodic flag or interrupt MICROCONTROLLER TIMERS 0 & 1 4

5 Timer Modes (cont'd) - Timer Mode 3 : Splits timer 0 into two 8-bit counter/timers. First counter (TLO) acts like mode 0, without prescaler. Second counter (TH0): Counts CPU cycles. Uses TR1 (timer 1 run bit) as enable. Uses TF1 (timer 1 overflow bit) as flag. Uses Timer 1 interrupt. Timer 1 (when timer 0 is in mode 3 ): Counter stopped if in mode 3. Running in mode 0, 1, or 2. Has gate (INT1) and external input (T1), but no flag or interrupt. May be used as a baud rate generator MICROCONTROLLER TIMERS 0 & 1 5

6 Counter/Timer in 16-bit (Mode 1) Osc. 12 TR1 T1 (Pin) Control TL1 8-bits TH1 8-bits TF1 Interrupt Gate INT1 (Pin) The Gate input controls whether the Counter runs while gated by the interrupt signal or not MICROCONTROLLER TIMERS 0 & 1 6

7 TMOD : Counter/Timer Mode Register GATE C/T M1 M0 GATE C/T M1 M0 Timer 1 Timer 0 - GATE : Permits INTx pin to enable/disable counter. - C/T : Set for counter operation, reset for timer operation. - M1, M0 : 00 : Emulate 8048 counter/timer (13-bits). 01 :16-bit counter/timer. 10 : 8-bit auto-reload mode 11 :Timer 0 = two 8-bit timers. Timer 1 = Counting disabled. Timing function allowed. (Can be used as Baud Rate generator) MICROCONTROLLER TIMERS 0 & 1 7

8 TCON : Counter/Timer Control Register TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0 - TF1, TF0 : Overflow flags for Timer 1 and Timer 0. - TR1, TR0 : Run control bits for Timer 1 and Timer 0. Set to run, reset to hold. - IE1, IE0 : Edge flag for external interrupts 1 and 0. * Set by interrupt edge, cleared when interrupt is processed. - IT1, IT0 : Type bit for external interrupts. * Set for falling edge interrupts, reset for 0 level interrupts. * = not related to counter/timer operation MICROCONTROLLER TIMERS 0 & 1 8

9 Interrupt System - 5 Interrupt Sources (in order of priority): External Interrupt 0. Timer 0. External Interrupt 1. Timer 1. Serial Port. - Each interrupt can be enabled separately. - Each interrupt type has a separate vector address. - Each interrupt type can be programmed to one of two priority levels. - External interrupts can be programmed for edge or level sensitivity MICROCONTROLLER TIMERS 0 & 1 9

10 IE : Interrupt Enable Register EA ES ET1 EX1 ET0 EX0 - EA : Global interrupt enable. - ES : Serial interface. - ET1 : Timer 1. - EX1 : External interrupt 1. - ET0 : Timer 0. - EX0 : External interrupt = Disabled. - 1 = Enabled MICROCONTROLLER TIMERS 0 & 1 10

11 Interrupt Vector Addresses Source Address IE0 03H TF0 0BH IE1 13H TF1 1BH RI&TI 23H The 8051 starts execution at 0000H after Reset MICROCONTROLLER TIMERS 0 & 1 11

12 IP: Interrupt Priority Register PS PT1 PX1 PT0 PX0 - PS : Serial interface. - PT1 : Timer 1. - PX1 : External interrupt 1. - PT0 : Timer 0. - PX0 : External interrupt = Low priority. - 1 = High priority MICROCONTROLLER TIMERS 0 & 1 12

13 80C51 Coding: Ideas and Examples 8051 MICROCONTROLLER TIMERS 0 & 1 13

14 (1) Reading a Timer "on the Fly" ReadTimer: MOV ValH,TH0 ;Read initial timer high and low values. MOV ValL,TL0 MOV A,TH0 ;Read timer high byte again. CJNE A,ValH,ChkHigh ;Has it changed? SJMP RTEX ;If not, first sample is OK. ChkHigh: JB ValL.7,RTEX ;Otherwise, check low byte to see if it ; changed after the original high byte ; sample. MOV ValH,A ;If it did change, use second high byte ; sample. RTEX: RET 8051 MICROCONTROLLER TIMERS 0 & 1 14

15 (2) Pulse Width Measurement Problem: measure the width of an input pulse.? start timer stop timer Assumption: use external interrupt 0 for the pulse input. Use timer 0 in gated mode. Note: to measure pulse low time in this manner, the input must be inverted externally MICROCONTROLLER TIMERS 0 & 1 15

16 (2) Pulse Width Measurement Setup: MOV TMOD,#09h ;Timer 0 gate on, in mode 1. MOV TCON,#01h ;Set INT0 to edge triggered mode. MOV TH0,#0 ;Clear timer 0 for measurement. MOV TL0,#0 SETB TR0 ;Start timer in gated mode. SETB EX0 ;Enable external interrupt 0. SETB EA ;Enable global interrupts ;External interrupt 0 service routine. ExInt0: CLR TR0 ;Stop timer. MOV ValH,TH0 ;Save timer value. MOV ValL,TL0 MOV TH0,#0 ;Clear timer 0 for measurement. MOV TL0,#0 SETB TR0 ;Restart timer. RETI 8051 MICROCONTROLLER TIMERS 0 & 1 16

17 (3) Pulse Period Measurement Problem: measure the period of an input pulse.? start timer stop timer Assumption: use external interrupt 0 for the pulse input. Note: this method may entail some loss of precision due to the possibility of variable interrupt latency MICROCONTROLLER TIMERS 0 & 1 17

18 (3) Pulse Period Measurement Setup: (same as previous example, but leave timer gate function turned off) MOV TMOD,#01h ;Timer 0 in mode 1. ;External interrupt 0 service routine. ExInt0: CPL TR0 ;Complement the timer run flag. This starts ; and stops the timer on alternate interrupts. JB TR0,INT0EX ;Exit if timer is running. MOV ValH,TH0 ;Otherwise sample the timer value. MOV ValL,TL0 MOV TH0,#0 ;Clear timer so another sample can MOV TL0,#0 ; be taken. INT0EX: RETI 8051 MICROCONTROLLER TIMERS 0 & 1 18

19 (4) Creating an Output Pulse Problem: create a pulse of known duration on a port pin. timer start pulse, timer stop pulse Assumption: use any spare port bit for the output. Note: the precision of pulses generated using this method will vary depending on the interrupt latency of the timer interrupt MICROCONTROLLER TIMERS 0 & 1 19

20 (4) Creating an Output Pulse Setup: MOV TCON,#0h ;Make sure timer is stopped. MOV TMOD,#01h ;Set timer to mode 1. MOV TH0,#HiTime ;Load timer with pulse duration. The value is the MOV TL0,#LoTime ; two's complement of the number of machine ; cycles to use for the pulse width. SETB TR0 ;Start timer. SETB P2.0 ;Start pulse (use CLR for a low going pulse). ;Tiimer 0 interrupt routine. T0INT: CLR P2.0 ;End of pulse (use SETB for a low going pulse). CLR TR0 ;Stop timer. RETI 8051 MICROCONTROLLER TIMERS 0 & 1 20

21 (5) Programming a PWM Output Problem: create a PWM output on a port pin. set timer low time set timer high time repeat Note: the precision of pulses generated using this method will vary depending on the interrupt latency of the timer interrupt MICROCONTROLLER TIMERS 0 & 1 21

22 (5) Programming a PWM Output T0INT: CLR TR0 ;Stop timer. CPL P2.0 ;Toggle output bit. JB P2.0,SetPWMHigh ;Is current phase high or low? MOV TH0,PWMLowH ;Set PWM low time. MOV TL0,PWMLowL SJMP T0EX SetPWMHigh: MOV TH0,PWMHighH ;Set PWM high time. MOV TL0,PWMHighL T0EX: SETB TR0 ;Restart timer. RETI Note: for higher frequency pulses, it may be possible to use the timer reload feature (mode 2) to obtain more accurate pulse durations MICROCONTROLLER TIMERS 0 & 1 22