K25C81-FB Datasheet, PDF (3/12 Pages) Semtech Corporation – Versatile PC/XC/AT/PS/2 Compatible Keyboard Encoder

FUNCTIONAL DESCRIPTION
The FlexiCoder^TM consists of six
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.
PIN DEFINITIONS
Mnemonic DIP
Vcc
40
Vss
20
OSCI
39
OSCO
38
_RESET
1
_IRQ
2
VX
3
RP
6
KC
8
KD
7
EKD
10
EKC
9
EKC1
37
C0-C7
C8-C15
C16
C17
12-19
28-21
11
4
R0-R5
R6
R7
NC
29-34
5
36
35
PLCC
44
22
43
42
1
2
4
7
9
8
11
10
41
3-17
18
19-21
31-24
12
5
32-37
6
39
38, 3
18, 23
40
QFP
38
17
37
36
41
42
43
2
4
3
6
5
35
8-15
26-18
7
44
27-32
1
34
16, 33
22, 39
40
TYPE
I
I
I
O
I
I
I
I
I/O
I/O
I/O
I/O
I
O
O
I/O
I
I
I
-
-
Name and Function
Power Supply: +5V
Ground
Oscilator Input
Oscilator Output
Reset: apply 0 V to provide orderly
start-up.
Must be tied to Vcc
Tie to Vcc.
Rollover Mode Selection: tie to
Vcc to select N-Key Rollover. Tie to
Ground to select Two-Key Inhibit
Mode.
Keyboard Clock: connects to PC’s
keyboard port Clock Line.
Keyboard Data: connects to PC’s
keyboard port Data Line.
External Keyboard Data:
connects to external keyboard Data
Line.
External Keyboard Clock:
connects to external keyboard Clock
Line.
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.
Column Select Outputs: select
one of columns.
Keyboard type selection: this pin
is used both as outputs for column
select and as input for standard
keyboard-type selection.
Row data inputs
No Connects: these pins are
unused.
Note: An underscore before a pin mnemonic denotes an active low signal.
Copyright Semtech, 1997-2001
3
DOC5-C81-DS-105
www.semtech.com