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Bài giảng Microprocessing Systems - Chapter 4: Timer operation - Lê Chí Thông

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ĐH Bách Khoa TP.HCM  
Lê Chí Thông  
The 8051 Microcontroller  
Chapter 4  
Timer Operation  
Lê Chí Thông  
[email protected].vn  
sites.google.com/site/chithong  
Ho Chi Minh City University of Technology  
Lê Chí Thông  
1
Review of 3-bit Up Counter  
000ꢀ001ꢀ…ꢀ111ꢀ000  
2
Overflow  
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1
ĐH Bách Khoa TP.HCM  
Lê Chí Thông  
Timer/Counter  
• 8051 has 2 timers  
– Timer 0  
– Timer 1  
• Each Timer is a 16-bit up counter  
– Counts from 0000H to FFFFH  
– FFFFH-to-0000H overflow: overflow flag is set  
Timer Clock  
Lê Chí Thông  
3
Timer/Counter  
• 3 Functions  
1. Timer is used as time delay generator (interval  
timing)  
– Internal clock source  
2. An event counter (event counting)  
– External clock source  
– For example :  
•
•
•
number of people passing through an entrance  
number of wheel rotations  
any other event that can be converted to pulses  
3. Baud rate generation for serial port  
Lê Chí Thông  
4
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2
ĐH Bách Khoa TP.HCM  
Lê Chí Thông  
Clock Source  
Internal clock fCLK = fCrystal / 12  
to Timer  
External clock  
C/T  
Clock  
Function  
0
1
Internal Timer (interval timing, delay)  
External Counter (event counting)  
Lê Chí Thông  
5
Timer 1 mode 1 (16 bit)  
Lê Chí Thông  
6
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3
ĐH Bách Khoa TP.HCM  
Lê Chí Thông  
Clock Enable/Disable  
Clock Enable/Disable  
Gate TRx  
INTx Function  
0
1
0
1
X
X
X
1
Clock Disable ꢀ Timer Stops  
0
1
Clock Enable ꢀ Timer Runs  
Clock Disable ꢀ Timer Stops  
Clock Enable ꢀ Timer Runs  
TRx: Bit TR0 or TR1; INTx: pin INT0 or pin INT1  
Lê Chí Thông  
7
Timer Run/Stop  
Gate TRx  
0
INTx Function  
X
X
X
1
Clock Disable ꢀ Timer Stops  
0
1
Clock Enable ꢀ Timer Runs  
Clock Disable ꢀ Timer Stops  
Clock Enable ꢀ Timer Runs  
0
1
1
•
•
When Gate is cleared (0)  
•
Timer runs when TRx = 1  
Timer stops when TRx = 0  
•
When Gate is set (1)  
•
Timer runs when TRx = 1 and signal at pin INTx goes high  
Timer stops when TRx = 0 or signal at pin INTx goes low  
•
TRx: Bit TR0 or TR1; INTx: pin INT0 or pin INT1  
Lê Chí Thông  
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4
ĐH Bách Khoa TP.HCM  
Lê Chí Thông  
GATE bit: More details  
• GATE=0  
• Internal control  
• The start and stop of the timer are controlled by the software  
Ex: SETB TR1 ; Run Timer 1  
CLR TR1 ; Stop Timer 1  
• GATE=1  
• External control  
• The hardware way of  
starting and stopping  
the timer by software  
Timer Timer  
stops runs  
and an external source.  
• When GATE is set and TRx is set  
(SETB TRx), Timer runs only while the INTx pin is high.  
Lê Chí Thông  
9
Applications of Timer  
Gate C/T Application  
0
1
0
Delay  
0
1
Event counting; Frequency meter  
Pulse width meter  
Lê Chí Thông  
10  
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5
ĐH Bách Khoa TP.HCM  
Lê Chí Thông  
Timer Registers  
• TH0, TL0 registers  
• TH1, TL1 registers  
• TMOD register  
• TCON register  
Lê Chí Thông  
11  
Timer 0 and Timer 1 Registers  
Timer 0  
TH0  
TL0  
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0  
Timer 1  
TH1  
TL1  
D15 D14 D13 D12 D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0  
Lê Chí Thông  
12  
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ĐH Bách Khoa TP.HCM  
Lê Chí Thông  
TMOD Register  
TMOD: Timer Mode Register  
(MSB)  
(LSB)  
GATE C/T M1 M0 GATE C/T M1 M0  
Timer 1 Timer 0  
GATE  
C/T  
0 : Timer/counter counts only while TRx bit is set.  
1 : Timer/counter counts only while TRx bit is set and  
INTx pin is high  
0 :  
1 :  
Timer operation (clock : Machine cycle)  
Counter operation (clock : Tx input pin)  
Lê Chí Thông  
13  
M1, M0: mode setting bits  
M1 M0 Mode Operating mode  
13-bit timer mode  
0
0
1
0
1
0
0
1
2
8-bit THx + 5-bit TLx (x= 0 or 1)  
16-bit timer mode  
8-bit THx + 8-bit TLx  
8-bit auto-reload mode  
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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14  
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ĐH Bách Khoa TP.HCM  
Lê Chí Thông  
An Example  
TMOD: Timer Mode Register  
(MSB)  
(LSB)  
GATE C/T M1 M0 GATE C/T M1 M0  
Timer 1 Timer 0  
Find the value for TMOD if we want to program timer 0 in mode 2,  
use 8051 XTAL for the clock source, and use instructions to start  
and stop the timer.  
Solution:  
TMOD= 0000 0010 Timer 1 is not used.  
Timer 0, mode 2  
C/T = 0 to use internal clock source (timer)  
GATE = 0 to use internal (software) start and  
stop method.  
Lê Chí Thông  
15  
More Examples  
TMOD: Timer Mode Register  
(MSB)  
(LSB)  
GATE C/T M1 M0 GATE C/T M1 M0  
Timer 1 Timer 0  
Ex:  
MOV TMOD,#00000001B ; Timer 0 mode 1, timer operation  
MOV TMOD,#20H ; Timer 1 mode 2, timer operation  
MOV TMOD,#12H ; Timer 1 mode 1, Timer 0 mode 2, both timer  
; operation  
MOV TMOD,#00000101B ; Timer 0 mode 1, counter operation  
MOV TMOD,#00001001B ; Timer 0 mode 1, external control (GATE=1)  
Lê Chí Thông  
16  
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ĐH Bách Khoa TP.HCM  
Lê Chí Thông  
4 Timer Modes  
Mode 0 : 13-bit counter  
(4048 mode)  
Mode 1 : 16-bit counter  
Mode 2 : 8-bit auto reload counter  
Mode 3 : two 8-bit counter  
the other counter will not  
output overflow (interrupt)  
Lê Chí Thông  
17  
TCON Register (1)  
• Timer control register: TCON  
– Upper nibble : timer/counter  
– Lower nibble : interrupts  
• TR (run control bit)  
– TR0 : Timer/counter 0  
– TR1: Timer/counter 1.  
– Turn timer/counter on/off.  
• TR=0: off (stop)  
• TR=1: on (start)  
(MSB)  
(LSB)  
TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0  
Timer 1  
Timer0  
for Interrupt  
Lê Chí Thông  
18  
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9
ĐH Bách Khoa TP.HCM  
Lê Chí Thông  
TCON Register (2)  
• TF (timer overflow flag)  
– TF0 : for Timer/counter 0  
– TF1 : for Timer/counter 1.  
– Originally, TF=0. When TH-TL roll over to 0000 from  
FFFFH (overflow), the TF is set to 1.  
• If we enable interrupt, TF=1 will trigger ISR.  
(MSB)  
(LSB)  
TF1 TR1 TF0 TR0 IE1 IT1 IE0 IT0  
Timer 1 Timer0 for Interrupt  
Lê Chí Thông  
19  
Delay 100 µs using Timer 1 (12 MHz crystal)  
12 MHz Crystal ꢀ fCLK = 12MHz/12 = 1MHz  
ꢀ 1 MC = 1/1MHz = 1 μs  
TMOD 10H  
ꢀ tDelay = 100 μs = 100 MC  
TH1:TL1 -100  
ꢀ Use Timer 1 to count from -100 to 0  
• Timer 1 mode 1, timer operation ꢀ  
Run Timer 1  
TMOD = 00010000B or 10H  
• Initial count TH1:TL1 = -100  
-100 = FF9CH  
N
Overflow?  
(TF1=1?)  
ꢀ TH1 = FFH and TL1 = 9CH  
Y
Clear overflow flag  
Stop Timer 1  
Lê Chí Thông  
20  
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ĐH Bách Khoa TP.HCM  
Lê Chí Thông  
Delay 100 µs using Timer 1 (12 MHz crystal)  
MOV TMOD, #00010000B; Timer 1, mode1  
MOV TL1, #9CH  
MOV TH1,#0FFH  
SETB TR1  
; Initial count  
TMOD 10H  
; -100 = FF9CH  
; start Timer 1  
TH1:TL1 -100  
WAIT: JNB TF1, WAIT  
; wait for overflow  
; clear overflow flag  
Run Timer 1  
CLR  
CLR  
TF1  
TR1  
; stop Timer 1  
N
Note:  
Overflow?  
(TF1=1?)  
MOV TL1,#9CH = MOV TL1,#LOW(-100)  
MOV TH1,0FFH = MOV TH1,#HIGH(-100)  
WAIT: JNB TF1, WAIT = JNB TF1,$  
Y
Clear overflow flag  
Stop Timer 1
Lê Chí Thông  
Delay 25 µs using Timer 0 (24 MHz crystal)  
Your Turn!  
Lê Chí Thông  
22  
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ĐH Bách Khoa TP.HCM  
Lê Chí Thông  
Delay 25 µs using Timer 0 (24 MHz crystal)  
MOV TMOD, #01H  
; Timer 0, mode 1: 16 bit  
; Load high byte  
MOV TH0,#HIGH -50  
MOV TL0, #LOW -50  
SETB TR0  
; Load low byte  
; start Timer 0  
JNB TF0, $  
; wait for overflow  
; clear Timer 0 overflow flag  
; stop Timer 0  
CLR  
CLR  
TF0  
TR0  
Lê Chí Thông  
23  
10-Hz Square Wave  
Write a program using Timer 0  
to create a 10 Hz square wave on P1.0  
Timer 0 mode 1  
Initial count = -50,000  
Start Timer 1  
f = 10 Hz  
T = 100,000 μs  
tH tL  
tH = tL = 50,000 μs  
T
N
Overflow?  
(TF1=1?)  
Delay 50,000 μs  
Y
Clear overflow flag  
P1.0 NOT (P1.0)  
Stop Timer 1  
P1.0 NOT (P1.0)  
(schematic)  
Lê Chí Thông  
24  
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ĐH Bách Khoa TP.HCM  
Lê Chí Thông  
10-Hz Square Wave  
Write a program using Timer 0 to create a 10 Hz square wave on P1.0  
MOV TMOD, #01H ; Timer 0, mode 1 (16-bit timer mode)  
LOOP: MOV TH0, #HIGH(-50000); high byte of -50,000  
MOV TL0, #LOW(-50000) ; low byte of -50,000  
SETB TR0  
; start timer  
WAIT: JNB TF0, WAIT  
; wait for overflow  
; stop timer  
CLR  
CLR  
CPL  
TR0  
TF0  
; clear timer overflow flag  
; toggle port bit  
; repeat  
P1.0  
SJMP LOOP  
Delay 50,000 μs  
(source)  
P1.0 NOT (P1.0)  
Lê Chí Thông  
25  
10-kHz Square Wave  
Write a program using Timer 0 to create a 10 kHz square wave on P1.0  
Lê Chí Thông  
26  
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ĐH Bách Khoa TP.HCM  
Lê Chí Thông  
10-kHz Square Wave  
Write a program using Timer 0 to create a 10 kHz square wave on P1.0  
MOV TMOD, #01H ; Timer 0, mode 1 (16-bit timer mode)  
LOOP: MOV TH0, #HIGH(-50); high byte of -50  
MOV TL0, #LOW(-50); low byte of -50  
SETB TR0  
; start timer  
WAIT: JNB TF0, WAIT  
; wait for overflow  
; stop timer  
CLR  
CLR  
CPL  
TR0  
TF0  
P1.0  
; clear timer overflow flag  
; toggle port bit  
; repeat  
SJMP LOOP  
Delay 50 μs  
Mode 1: 16-bit timer  
P1.0 NOT (P1.0)  
Lê Chí Thông  
27  
10-kHz Square Wave using Mode 2  
Write a program using Timer 0  
to create a 10 kHz square wave on P1.0  
Timer 0 mode 2  
Reload value = -50  
Start Timer 1  
Mode 2: 8-bit auto-reload timer  
N
Overflow?  
(TF1=1?)  
Delay 50 μs  
Y
Clear overflow flag  
P1.0 NOT (P1.0)  
P1.0 NOT (P1.0)  
Lê Chí Thông  
28  
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14  
ĐH Bách Khoa TP.HCM  
Lê Chí Thông  
10-kHz Square Wave using Mode 2  
Write a program using Timer 0 to create a 10 kHz square wave on P1.0  
MOV TMOD, #02H ; Timer 0, mode 2 (8-bit auto-reload)  
MOV TH0, #-50  
SETB TR0  
; reload value  
; start timer  
WAIT: JNB TF0, WAIT  
; wait for overflow  
; clear timer overflow flag  
; toggle port bit  
; repeat  
CLR  
CPL  
TF0  
P1.0  
SJMP WAIT  
Mode 2: 8-bit auto-reload timer  
29  
Buzzer Interface  
A buzzer is connected to P1.7 and a debounced switch is connected  
to P1.6. Write a program that reads the logic level provided by the  
switch and sounds the buzzer for 1 second for each 1-to-0 transition  
detected.  
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30  
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Lê Chí Thông  
Buzzer Interface  
DELAY: MOV R7,#HUNDRED  
AGAIN: MOV TH0,#HIGH COUNT  
HUNDRED EQU 100  
COUNT EQU -10000  
MOV TL0,#LOW COUNT  
SETB TR0  
JNB TF0,$  
CLR TF0  
CLR TR0  
DJNZ R7,AGAIN  
RET  
END  
ORG 0000H  
MOV TMOD, #01H  
LOOP: JNB P1.6, LOOP ;wait for high level  
WAIT: JB P1.6, WAIT ;wait for low level  
SETB P1.7  
CALL DELAY  
CLR P1.7  
SJMP LOOP  
Lê Chí Thông  
31  
Reading a timer “On the Fly”  
• When reading the content of counter, is the data correct?  
• 16-bit timer/counter, but 8-bit reading (MOV instruction)  
ꢀ 2 read operations  
ꢀ A “phase error” may occur.  
• Solution  
AGAIN:MOV A, TH1  
MOV R6, TL1  
CJNE A, TH1, AGAIN  
MOV R7, A  
Lê Chí Thông  
32  
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Lê Chí Thông  
Techniques for Programming Timed Intervals  
• 12 MHz operation  
Maximum  
interval [μs]  
Technique  
≈10  
Software tuning  
256  
8-bit timer with auto-reload  
16-bit timer  
65536  
No limit  
16-bit timer plus software loops  
Lê Chí Thông  
33  
Very Short Intervals  
Very short intervals (i.e. high frequencies) can be  
programmed without using timers.  
LOOP:  
SETB P1.0  
CLR P1.0  
SJMP LOOP  
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34  
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Lê Chí Thông  
Delay 1 s using Timer 1 (12 MHz crystal)  
• 1 s delay subroutine: 1 s = 20 x 50 ms  
MOV  
…
TMOD, #00010000B  
; Timer 1, mode1  
DELAY1S:  
PUSH 07  
MOV R7,#20  
; Push R7 to stack  
; 20 loops  
LOOP: MOV  
MOV  
SETB  
JNB  
TL1, #LOW(-50000)  
; Initial count = -50000  
;
TH1,#HIGH(-50000)  
TR1  
; start Timer 1  
; wait for overflow  
; clear overflow flag  
; stop Timer 1  
TF1, $  
TF1  
CLR  
CLR  
TR1  
DJNZ  
POP  
R7,LOOP  
07  
; Pop R7 from stack  
RET  
Lê Chí Thông  
35  
Counter Operation  
Internal clock fCLK = fCrystal / 12  
to Timer  
C/T  
0
Clock  
Function  
Internal Timer (interval timing, delay)  
Lê Chí Thông  
36  
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Lê Chí Thông  
Counter 0 Mode 1  
• C/T = 1  
• 16-bit counter (TH0 and TL0)  
• TH0-TL0 is incremented when TR0 is set to 1 and an external  
pulse (in T0) occurs.  
Timer 0  
external clock  
input  
Overflow  
flag  
TH0  
TL0  
TF0  
(P3.4/T0)  
TF0 goes high  
when FFFF ꢀ 0  
C/T = 1  
TR0  
Lê Chí Thông  
37  
Counter_BarLED  
A push button is connected to P3.4 (T0). Assume that there is no  
contact bounce. Write a program that counts the pulses created by  
push button and display on the LED-Bargraph connected to Port 1.  
(schematic)  
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38  
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ĐH Bách Khoa TP.HCM  
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Counter_BarLED  
ORG 0000H  
MAIN:  
MOV TMOD,#00000101B;Timer 0, 16 bit, external clock  
;(counter operation)  
;Gate=0, C/T=1, M1 M0 = 01  
MOV TH0,#0  
MOV TL0,#0  
SETB TR0  
;Start Timer  
LOOP: MOV A,TL0  
MOV P1,A  
SJMP LOOP  
END  
;Read Timer  
;Display on Bar-LED  
(source)  
Lê Chí Thông  
39  
Counter_7segLED  
A push button is connected to P3.4 (T0). Assume that there is no  
contact bounce. Write a program that counts the pulses created by  
push button and display on the common-anode 7-segment LED  
connected to Port 1. (schematic)  
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40  
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