Bài gi ng K thu t Vi x lý
Ngành i n t -Vi n thông
i h c Bách khoa à N ng
c a H Vi t Vi t, Khoa TVT
Tài li u tham kh o
[1] K thu t vi x lý, Văn Th Minh, NXB Giáo d c, 1997
[2] K thu t vi x lý và L p trình Assembly cho h vi x
lý, Xuân Ti n, NXB Khoa h c & k thu t, 2001
Chương 6
Các ki u I/O
6.1 Thăm dò (Polling)
6.2 I/O i u khi n b ng ng t (Interrupt)
-
6.3 DMA (Direct Memory Access)
Thăm dò
A19 5V
A18
:
A0
D7 A0 B0
D6 A1 B1
D5 A2 B2
D4 A3 B3
D3 A4 B4
D2 A5
74LS245 B5
8088 D1 A6 B6
Minimum D0 A7 B7
Mode
E DIR
IOR
IOW
mov dx, F000
L1: in al, dx
cmp al, FF
je L1
A A A A A A A A A A A A A A A A IOR :
1111119876543210
543210 :
A19 5V
A18
: The Circuit
A0
D7 A0 B0
D6 A1 B1
D5 A2 B2
D4 A3 B3
D3 A4 B4
D2 A5
74LS245 B5
8088 D1 A6 B6
Minimum D0 A7 B7
Mode
E DIR
D0 Q0
D1 Q1
IOR
D2 Q2
IOW D3 Q3
D4 Q4
D574LS373
Q5
D6 Q6
D7 Q7
A A A A A A A A A A A A A A A A IOR LE OE
1111119876543210
543210
AAAAAAAAAAAAAAAAIOW
1111119876543210
543210
Bài toán
• Chương trình t o ra hi u ng “LED ch y”:
- Ban u LED ch y t trên xu ng
- Khi nh n phím th p nh t thì LED thay i
hư ng ch y
- Khi nh n phím cao nh t thì chương trình
k t thúc
Chương trình
mov dx, F000 L4: mov bl, al
mov ah, 00
in al, dx
mov al, 01
cmp al, FF
L1: out dx, al
je L6
mov cx, FFFF
L2: dec cx test al, 01
jnz L2 jnz L5
cmp ah, 00 xor ah, FF
jne L3 jmp L6
rol al, 1 L5: test al, 80
cmp al, 01 jz L7
jne L1 L6: mov al, bl
jmp L4 jmp L1
L3: ror al, 1
L7:
cmp al, 80
jne L1
What’s the problem with polling
in the sample program?
• Running LED takes time
• User might remove his/her finger from the
switch
• before the in al, dx instruction is
executed
• the microprocessor will not know that the
user has pressed the button
Problem with Polling
mov dx, F000 L4: mov bl, al
mov ah, 00 in al, dx
mov al, 01 cmp al, FF
L1: out dx, al je L6
mov cx, FFFF
test al, 01
L2: dec cx
jnz L5
jnz L2
xor ah, FF
cmp ah, 00
jne L3 jmp L6
rol al, 1 L5: test al, 80
cmp al, 01 jz L7
jne L1 L6: mov al, bl
jmp L4 jmp L1
L3: ror al, 1 L7:
cmp al, 80
jne L1
Interrupt
• The microprocessor does not check if data
is available.
• The peripheral will interrupt the processor
when data is available
Polling vs. Interrupt
instruction
While studying, I’ll Input Memory
check the bucket every 5 Device
minutes to see if it is
already full so that I can
transfer the content of
the bucket to the drum.
µP
POLLING
Polling vs. Interrupt
instruction
I’ll just study. When the Input Memory
speaker starts playing Device
music it means that the
bucket is full. I can then
transfer the content of
the bucket to the drum.
Interrupt
request
µP
INTERRUPT
Copyright by webtailieu.net