This document discusses the architecture of simple I/O devices including a hex keyboard and LED display using an 8279 keyboard-display interface. It describes the components and working of a keyboard including mechanical and membrane key switches. It also discusses LED displays for numerical and alphanumeric characters including 7-segment, 18-segment, and matrix displays. Finally, it provides details on the 8279 controller which interfaces the keyboard and LED display with a microprocessor, describing its keyboard, display and MPU interface sections.

1. JAI NARAIN VYAS UNIVERSITY
JODHPUR ( RAJ. )
PHYSICS DEPARTMENT
PRESENTEDBY –
RAMNIWAS JAKHAR
SUBMITTEDTO :– DR.
s. k. sharma sir
DIGITAL ELECTRONICS AND
MICROPROCESSOR

2. ARCHITECTURE OF
SIMPLE I/O DEVICES :
HEX KEYBOARD, LED
DISPLAY WITH 8279
KEYBOARD-DISPLAY
INTERFACE

3. 1. Keyboard
2. LED-Display
3. Hex keyboard , LED display with 8279
keyboard- display interface .
1. Keyboard :-
(1) Key switches :-
a. Mechanical key switches :-
- When plunzor is press, than movable plate take
physical contact with fitted metallic flate.
- When press than it’s set or 1.
- When key is remove, key return their original
position due to string.

4. • Disadvantage :- collision
of two metallic plate, it
take some time to settle
down , and time is known
as settle time.

5. b. Membrane key switches :-
- Sheet A : for column collector.
- Sheet B : Sheet with whole.
- Sheet C : for row collector.
- for every key, a particular whole sheet.

6. (2) Arrangement of key’s :-
- Key’s are arrange in matrix format.
- Microprocessor have 4x5 matrix key’s
arrangement.
- O/P port :- Port where m.p. sent data.
- I/P port :- Place where m.p. receive data.
- M.P. sent zero’s to 4-row’s.
- whenever a key is pressed, mean set, than m.p.
scan it, and get a binary code, for a particular
key.

8. 2. LED DISPLAY :-
LED for display purpose.
(1) Types of LED for Display :-
a. 7- Segment :-
The 7- Segment display consists of seven LED’s
arranged in a rectangular fashion.
Called Segment because when illuminated the
Segment form part of a numerical digit, to be
displayed. Use :- numerous and few alphabets.

9. b. 18- Segment display :-
18- Segment display can be use for alpha
numerous and few special characters.
c. Matrix arrangement :- All alpha numerous and
special characters.

10. 3. Hex keyboard , LED display with 8279
keyboard- display interface :-
8279 Hex keyboard and display controller :-
-8279 controller, packed in 40 pin dual in packed IC.
- Give interface to keyboard and 7- Segment LED
display with Intel microprocessor.
- 8279 can be divided into 3-parts :-
(1). Key board section.
(2). Display section.
(3). MPU interface unit.

12. (1). Key board section :-
In brief, 8279 KB section work is classified into
3 modes –
a. Scanned Keyboard Mode
b. Scanned Sensor Matrix
c. Stored Input .
(2). Display section :-
It deals with the output mode display-related
operations. This mode is further classified into two
output modes :
a. Display Scan
b. Display Entry .

13. (3) MPU interface unit :-
MPU interface consists of 8-bit bi-directional
data buffer bus.
I/O control : pins –
a. A0 : Used for distinguish between command
and data.
b. RD, WR : Status or read/ write operation.
c. by use of CS Low, device select by m.p.

14. Pin diagram
of 8279
controller

15. THANK YOU