Bài giảng Vi xử lý - Chương 5: Thiết kế hệ vi xử lý

 BC337/338 has a minimum hFE of 100 (at 
100mA), we'll need to provide it with at least 50mA/100 = 0.5mA of base 
current.
In practice, you give it roughly double this value, say 1mA of base current, just 
to make sure it does saturate. So if your resistance will be TTL Logic High 
Voltage (Min) /1ma ( 1K approx)
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Example 2 – Switch and LED
Connection 
Port 0 is connected to eight 
LEDs, each of them is 
connected to 5V through a 
330ohm resistor. Port 1 is 
connected to a DIP switch and a 
10Kohm resistor
Condition 
Corresponding LED should light 
up when switch pressed , i.e. if 
Switch at 1.0 is pressed -> LED 
at P0.0 should light up.
Solution:
; To configure port 1 for input.
MOV P1, #0FFH
LOOP: MOV A, P1
MOV P0, A
SJMP LOOP ; Stay in 
;infinite loop
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Using ULN (Driver IC)
Another option for driving relays would be to use a high-voltage, high-current, 
Darlington array driver IC such as the ULN2803. The ULN2803 can directly 
interface to the data outputs of the 8051 pins, and provides much higher 
drive-current. The ULN2803 also has internal diode protection that eliminates 
the need for the fly-back diode as shown in the above relay driver schematics. 
You can connect 8 relay using this IC.
So ULN is better choice if you have more than 3 relay. ( Simple design of 
circuit & PCB as well ! )
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7 Segment Display
INTRODUCTION
For the seven segment display you can use the LT-541 or LSD5061-
11 chip (etc). Each of the segments of the display is connected to 
a pin on the 8051 (the schematic shows how to do this). In order to 
light up a segment on the the pin must be set to 0V. To turn a 
segment off the corresponding pin must be set to 5V. This is simply 
done by setting the pins on the 8051 to '1' or '0'.
LED displays are
– Power-hungry (10ma per LED)
– Pin-hungry (8 pins per 7-seg display)
But they are cheaper than LCD display
7-SEG Display are available in two types: Common anode (CA) & 
common cathode (CC), but command anode display are most 
suitable for interfacing with 8051 since 8051 port pins can sink 
current better than sourcing it.
108
7 Segment Display
dp = decimal point
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The 7-segment Display (Cont.)
• 7-segment displays come in 2 configurations:
Common Anode (CA) Common Cathode (CC)
• As we have seen, it would be preferable to connect 
the cathode of each diode to the output pin.
• Therefore, the common anode variety would be 
better for our interfacing needs.
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Interfacing a 7-segment display 
• Also, as seen with interfacing the LED, a resistor will be 
needed to control the current flowing through the diode.
– This leaves two possibilities:
– Case 2 would be more appropriate as case 1 will produce 
different brightness depending on the number of LEDs turned 
on.
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Use of current buffer
• Interfacing to a DIP switch and 7-segment display
• Output a ‘1’ to ON a segment
• We can use 74244 to common cathode 7_seg 
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BCD to 7-Seg lookup table
mov p3,#0fh
mov a,p3
anl a,0fh
get_code: mov DPTR, #7s_tab
movc A, @A+DPRT
mov p1,a
7s_tab: db 3fh,30h,5bh,4fh,66h
db 6dh,7dh,07h,7fh,6fh
END
a
b
c
f
e
d
f
e
a
b
e
g
d
a
b
c
g
d
b
c
f
g
a
c
f
g
d
a
c
f
e
g
d
a
b
c
a
b
c
f
e
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d
a
b
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d
BCD p g f e d c b a
7_seg
he
x
0000 0 0 1 1 1 1 1 1 3f
0001 0 0 1 1 0 0 0 0 30
0010 0 1 0 1 1 0 1 1 5b
0011 0 1 0 0 1 1 1 1 4f
0100 0 1 1 0 0 1 1 0 66
0101 0 1 1 0 1 1 0 1 6d
0110 0 1 1 1 1 1 0 1 7d
0111 0 0 0 0 0 1 1 1 07
1000 0 1 1 1 1 1 1 1 7f
1001 0 1 1 0 1 1 1 1 6f
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Creating Digit Pattern
with 7-segment LED Display
For displaying Digit say 7 we need to light segments: a ,b, c. Since 
we are using Common anode display , to do so we have to to provide 
Logic 0 (0 v) at anode of these segments.
So need to clear pins: P1.0 ,P1.1,P1.2. that is 1 1 1 1 1 0 0 0  F8h .
Connection
Hex Code
You can also do this for some characters like A ,E .. but not for D or B because it will be 
same as that of 0 & 8 . So this is one of limitation of 7-seg display.
Since we can Enable only one 7-seg display at a time ,we need to scan these display at 
fast rate .The scanning frequency should be high enough to be flicker-free. At least 30HZ 
.Therefore – time one digit is ON is 1/30 seconds
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INTERFACING TO LED DISPLAY (1/2)
Note that we are using Common Anode display. so the common Anode pin 
is tied to 5v .The cathode pins are connected to port 1 through 330 Ohm 
resistance (current limiting).
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INTERFACING TO LED DISPLAY (2/2)
Connection: a:h to port p1.0:p1.7 , D0:D1 to p3.0:p3.1.
To Display: Consider example of vending machine where we want to 
display number of soft drink bottles on display entered by customer. 
Suppose he enter 3 (03) bottles then we will use lookup table to
see DIGIT PATTERN of these keys.
So DIGI[1]=C0 (hex code for '0') &
DIGI[2]=B0(hex code for '3').
Algorithm
start : Disable [D0:D1]
again : Enable D0
[a:h] - pattern for Digit1
Delay
Disable D0. 
Enable D1
[a:h] - pattern for Digit2
Delay
Goto again
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Hiển thị quét LED với 4 LED 7 đoạn
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Chú ý với hiển thị dồn kênh
Với hiển thị LED dồn kênh:
• Ở mỗi thời điểm chỉ có một hiển thị LED 7 đoạn được cho 
phép (qua các khóa điện tử BJT).
• Các ngõ vào a-h nối chung với nhau cho tất cả các LED 7 
đoạn.
• Tổng số chân cổng cần sử dụng là 8 + số ký số (digit), với thí 
dụ hình 5.80 thì tổng số chân là 8 + 4 = 12.
• Tần số quét phải đủ cao để tránh tình trạng thấy LED nhấp 
nháy:
• tối thiểu 40Hz
• thời gian cho 1 digit sáng là 1/40 giây.
• tần số quét cao hơn thì sẽ giảm sự nhấp nháy
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TD: Mạch hiển thị LED 7 đoạn của 
www.MightyMicons.com
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Mạch này dùng LED 7 đoạn loại 
nào? (CA hay CC)
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Một số thí dụ với LED và phím nhấn
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Basic Output Techniques with LEDs
P1.7
P1.6
P1.5
P1.4
P1.3
P1.2
P1.1
P1.0
+5V
8051
EA VCC
Reset
XTAL1
XTAL2
VSS
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Example 3: Light-up LEDs
All LEDs ON
All LEDs OFF
1st: LEDs
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Program Listing for Example 3
ORG 0000H
CLR A
LOOP: MOV P1, A
CPL A
ACALL DELAY
AJMP LOOP
DELAY: MOV R6, #250
DL1: MOV R7, #200
DL2: DJNZ R7, DL2
DJNZ R6, DL1
RET
END
Start
Set A = 00
Move the content 
of A to P1
Delay for 0.1s
Invert the 
content of A
Assume 12MHz clock, determine the delay time.
Time delay, Tex1 = 1 + [ ( 1+ 200 * 2 ) + 2 ] * 250 + 2 = 100,753 MachineCycle
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Example 4: Lighting Sequence
ORG 0000H
START: MOV R1, #07H
MOV A, #11111110B
LEFT: MOV P1, A
ACALL DELAY
RL A
DJNZ R1, LEFT
;
MOV R1, #07H
MOV A, #01111111B
RIGHT: MOV P1, A
ACALL DELAY
RR A
DJNZ R1, RIGHT
AJMP START
;
DELAY: .
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Example 5: Use a Look-up Table
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Program Listing of Example 5
ORG 0000H
START: MOV R0, #OKLUT+1 ; length of table
MOV DPTR, #LUT ; code start address
MOV R1, #00H
LOOP: MOV A, R1
MOVC A, @A+DPTR
MOV P1, A
ACALL DELAY
INC R1 ; point to next data of table
DJNZ R0, LOOP ; finish ?
AJMP START
;
DELAY:
; do not modify the value in register R0, & R1
; DELAY = 1 + (100751 + 2 ) * 2 + 2 = 201,509 Machine Cycle !
MOV R5, #2
DL1: MOV R6, #250
DL2: MOV R7, #200
DL3: DJNZ R7, DL3
DJNZ R6, DL2
DJNZ R5, DL1
RET
;
LUT: DB 01111110B
DB 00111100B
DB 00011000B
DB 00000000B
DB 00011000B
DB 00111100B
DB 01111110B
DB 11111111B
;
DB 01111110B 
DB 00111100B
DB 00011000B
DB 00000000B
DB 00011000B
DB 00111100B
DB 01111110B
DB 11111111B
;
DB 00000000B
DB 11111111B
DB 00000000B
OK: DB 11111111B
END
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Example 6: Basic Input Technique
P1.7
P1.6
P1.5
P1.4
P1.3
P1.2
P1.1
P1.0
+5V
8051
EA VCC
Reset
XTAL1
XTAL2
VSS
P3.7
P3.6
P3.5
P3.4
SW1
SW2
SW3
SW4
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Example 6
When SW1 Closed
When SW3 Closed When SW4 Closed
When SW2 Closed
Priority: SW1 SW2 SW3 SW4
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Flow Chart of Example 6
Start
Initialization
Set P3 as input port
Read SW1SW4 status
SW1 closed?
SW2 closed?
SW3closed?
SW4 closed?
SW1 Handler
Y
SW2 Handler
Y
SW3 Handler
Y
SW4 Handler
Y
2
1
21
N
N
N
N
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Program Listing of Example 6
ORG 0000H
MOV R1, #00000000B
MOV R2, #01010101B
MOV R3, #00001111B
MOV R4, #11110000B
;
TEST: ORL P3, #0FFH 
; P3 is configured as input port!
JNB P3.7, CASE1
JNB P3.6, CASE2
JNB P3.5, CASE3
JNB P3.4, CASE4
AJMP TEST
;
CASE1: MOV A, R1
MOV P1, A
ACALL DELAY
XRL A, #11111111B
MOV P1, A
AJMP TEST
;
CASE2: MOV A, R2
MOV P1, A
ACALL DELAY
XRL A, #10101010B
MOV P1, A
AJMP TEST
CASE3: MOV A, R3
MOV P1, A
ACALL DELAY
XRL A, #11110000B
MOV P1, A
AJMP TEST
CASE4: MOV A, R4
MOV P1, A
ACALL DELAY
XRL A, #00001111B
MOV P1, A
AJMP TEST
DELAY: ..
;inside DELAY, don’t modify A, R1, R2, R3 & R4.
RET
END
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Ex7: 7-Segment LED Numeric Display
R3 is used as a counter, write a 8051 assembly language program using 
look-up table method, to display the value in R3 to a 7-segment display
Eprom Version
Of 8051
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Program Listing of Example 7
ORG 0000H
MOV R3, #00H
LOOP: MOV DPTR, #TABLE
MOV A, R3
MOVC A, @A+DPTR
;
; Display numbers on 7-segment display
MOV P1, A
ACALL DELAY
;
; Increase R3 by 1 and loop back
MOV A, R3
ADD A, #1
DA A
ANL A, #0FH 
; take the lower nibble only
; now A has value between 0 to 9
MOV R3, A ;update R3
AJMP LOOP
;
DELAY: ..
RET
TABLE: DB 11000000B ; 0
DB 11111001B ; 1
DB 10100100B ; 2
DB 10110000B ; 3
DB 10011001B ; 4
DB 10010010B ; 5
DB 10000010B ; 6
DB 11111000B ; 7
DB 10000000B ; 8
DB 10010000B ; 9
;
END
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Một số thí dụ các mạch giao tiếp IO
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8031/8051 với LED và loa
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Giao tiếp với động cơ DC
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Giao tiếp với động cơ bước
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Giao tiếp với DAC
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Mạch loa đi kèm với DAC
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Mạch điều khiển động cơ DC đi 
kèm DAC
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Giao tiếp với ADC