K25C81-FB Semtech, K25C81-FB Datasheet - Page 3

• Manufacturer Part Number: K25C81-FB
• Description: Versatile PC/XC/AT/PS/2 Compatible Keyboard Encoder
• Manufacturer: Semtech

The FlexiCoder
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.
Copyright Semtech, 1997-2001
DOC5-C81-DS-105
FUNCTIONAL DESCRIPTION
TM
consists of six
Mnemonic
Vcc
Vss
OSCI
OSCO
_RESET
_IRQ
VX
RP
KC
KD
EKD
EKC
EKC1
C0-C7
C8-C15
C16
C17
R0-R5
R6
R7
NC
Note: An underscore before a pin mnemonic denotes an active low signal.
PIN DEFINITIONS
3
DIP
40
20
39
38
1
2
3
6
8
7
10
9
37
12-19
28-21
11
4
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
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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.