FUNCTIONAL DESCRIPTION

PIN DEFINITIONS

Copyright Semtech, 1997-2001

DOC5-C81-DS-105

www.semtech.com

3

Mnemonic

DIP

PLCC

QFP

TYPE

Name and Function

Vcc

40

44

38

I

Power Supply: +5V

Vss

20

22

17

I

Ground

OSCI

39

43

37

I

Oscilator Input

OSCO

38

42

36

O

Oscilator Output

_RESET

1

1

41

I

Reset: apply 0 V to provide orderly

start-up.

_IRQ

2

2

42

I

Must be tied to Vcc

VX

3

4

43

I

Tie to Vcc.

RP

672I

Rollover Mode Selection: tie to

Vcc to select N-Key Rollover. Tie to

Ground to select Two-Key Inhibit

Mode.

KC

894I/O

Keyboard Clock: connects to PC’s

keyboard port Clock Line.

KD

783I/O

Keyboard Data: connects to PC’s

keyboard port Data Line.

EKD

10

11

6

I/O

External Keyboard Data:

connects to external keyboard Data

Line.

EKC

9

10

5

I/O

External Keyboard Clock:

connects to external keyboard Clock

Line.

EKC1

37

41

35

I

External Keyboard Clock 2:

connects to external keyboard Clock

Line and is used to generate an

interrupt for every Clock Line transition.

This signal must be inverted for PC/XT

keyboards.

C0-C7

12-19

3-17

8-15

O

Column Select Outputs: select

18

one of columns.

19-21

C8-C15

28-21

31-24

26-18

C16

11

12

7

O

C17

4

5

44

I/O

Keyboard type selection: this pin

is used both as outputs for column

select and as input for standard

keyboard-type selection.

R0-R5

29-34

32-37

27-32

I

Row data inputs

R6

561I

R7

36

39

34

I

NC

35

38, 3

16, 33

-

No Connects: these pins are

18, 23

22, 39

-

unused.

40

40

Note: An underscore before a pin mnemonic denotes an active low signal.

major sections (see functional

diagram, previous page). These

are the Keyboard Encoder, the

Mode Control Unit, the PC

Communication Channel, the 8042

Emulation Channel, the Interrupt

Control Unit and the Data Buffer.

These sections communicate with

each other and operate

concurrently.

The controller continuously scans a

keyboard organized as an 8 row by

18 column matrix, for a maximum of

144 keys. Smaller-size keyboards

can be connected provided that all

unused row pins are connected to

Vcc. The microcontroller selects

one of the 18 column lines (C0-C17)

every 512 µS and then reads the

row data lines (R0-R7).

A key closure is detected as a zero

in the corresponding position of the

matrix. A complete scan cycle for

the entire keyboard takes approxi-

mately 9.2 mS. Each key press is

debounced for a period of 20 mS.

Once the key is verified, the

corresponding key code(s) are

loaded into the transmit buffer of

the PC Keyboard Communication

Channel.