1. Electronics Lab. 4 Exp. 2 : Parallel input
Prof. 박인철
T.A.

2. 실험 목적 Parallel input과 Parallel output의 사용법 이해 8255 PPI의 사용법 숙지
PPI programming방법에 대한 이해

3. 실험 내용 Display switch history Logic checker 스위치가 눌려진 횟수를 LED의 점멸로 표시
debouncing
점등시간 : 0.1초, 소등시간 : 0.4초
Logic checker
스위치의 상태를 LED로 표시

4. Parallel Interface Block Diagram
data bus
Inverter register
Red LED
PA0
IBM PC
ISA
BUS
Inverter register
Green LED
PA1
control signals
8255
PPI
+5V R
address
Logic
(design)
PB0
GND
8255 setting
mode 0
port A : output
port B : input

5. 8255 External Description
Microcomputer bus와 인터페이스하기 위한 general purpose I/O component
address bus
control bus
data bus
RD.WR
D7…D0
A0.A1
8255A B C A 8 4 4 8
11/09/’98

6. Operation Word Format
11/09/’98

7. Operation Definition Format
mode set flag
1=active
group B
mode selection
0=mode 0
0=mode 1
group A
mode selection
00=mode 0
01=mode 1
1x=mode2
port B
1=input
0=output
port A
1=input
0=output
port C (upper)
1=input
0=output
port C (lower)
1=input
0=output
11/09/’98

8. MODE 0
11/09/’98

9. MODE 1
11/09/’98

10. MODE 2
11/09/’98

11. Intel 8255 PPI control I/O port address Control Byte
0x318 : 8255 PPI port A
0x319 : 8255 PPI port B
0x31A : 8255 PPI port C
0x31B : 8255 PPI Control Byte
Control Byte
0x31B address에 입력되는 data에 의해 결정

12. Debouncing 스위치의 상태가 변화할 때 생기는 노이즈를 제거하는 방법
상태를 샘플링하는 주기가 충분히 빠를 때, 약간의 delay를 주고 여러 번 샘플링하여 상태값의 변화 과정을 보고 판단한다.
Ex) ® 0에서 1로 천이
switch signal
Debounced signal

13. Delay 설정 방법 Interrupt : 15H Service routine : 86H Registers on entry :
AH : 86H
CX : high-order value of delay time in microseconds
DX : low-order value of delay time in microseconds
Syntax :
MOV AH,86h ; delay service
MOV CX, ; high 16bit value
MOV DX, ; wait 1/100 second
INT 15h ; BIOS extension interrupt

14. 문제 1 순서도 Y N N Y N Y START counter ==0? Initialize 8255 PPI
Turn on LED N
done?
Delay 0.1s
Read the
switch Y
Display N blink
debouncing
Turn off LED N
END
Delay 0.4s
Transition? Y
Decrease counter
Increase counter

15. 문제 2 순서도 Y N 1 N Y Y N Red ON Green ON START set counter Initialize
8255 PPI Y
counter==0?
Read the
switch N
Logic State
Decrease counter
debouncing 1
Red ON
Green OFF
Red OFF
Green ON
Read the
switch N
Transition? Y
debouncing Y N
Transition?