FlexiCoder

K25C81

Versatile PC/XC/AT/PS/2 Compatible

Keyboard Encoder

FlexiCoder

is a trademark of Semtech Corp. All

other trademarks belong to their respective
companies.

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HID & SYSTEM MANAGEMENT PRODUCTS, KEYCODER

FAMILY

DESCRIPTION

FEATURES

_RESET

Vcc

OSCI

OSCO

EKC1

C10

C11

C12

C13

C14

C15

_IRQ

C17

EKC

EKD

C16

Vss

DIP

C17

_IRQ

_RESET

VCC

OSCI

OSC0

EKC1

KD
KC

EKC
EKD

C16

C0
C1
C2
C3
C4

R7
NC
R5
R4
R3
R2
R1
R0
C8
C9
C10

VSS

C15

C14

C13

C12

C11

EKC

EKD

C16

C17

_IRQ

_RESET

VCC

OSCI

OSCO

EKC1

C10

C11

VSS

C15

C14

C13

C12

PLCC

QFP

� Custom keyboards/keypads
� Control panels
� Automatic teller machines
� Embedded control systems
� Public Information Kiosks

� Instrumentation
� Test and Measurement equipment
� Point of Sales terminals
� Industrial Controllers
� Medical Instruments

� Enables custom keypad scan

codes to remain unaffected by
the Shift States of an external
keyboard

� Includes jumper-selectable auto-

repeat for designated keys

� Offers two-key inhibit scanning

mode

� Directly interfaces a PC

keyboard port

� Encodes up to 144 custom keys

on an 8 X 18 matrix

� Buffers up to 122 keycodes
� Interfaces to 83/101/102

standard keyboard or other
8042-compatible device

The FlexiCoder

is a versatile, low-

power keyboard encoder. It offers
two bi-directional channels for
communicating with a
PC/XT/AT/PS2 system, and/or any
optional keyboard-compatible
devices, such as an 83 or 101/102
standard desktop keyboard, OCR,
barcode reader, etc. The K25C81
directly interfaces a PC keyboard
port, making custom keyboard to
system communications fully
transparent.

On an 8 x 18 matrix, the
FlexiCoder

will scan, debounce

and encode up to 144 keys. Scan
codes corresponding to single keys
of the IBM 101 keyboard, or a
combination of these keys when
depressed with Shift, Ctrl, and Alt
keys, are generated with each key
press. Custom keypad input is not
effected by the Shift States of an
external keyboard.

Users can conveniently define key
assignments on the matrix as single
or repeating actions. All keys must
be released between key strokes or
scanning is suspended. The
encoder can buffer up to 122
keycodes, and control inputs and
outputs are provided for interfacing
with contact keyboards.

The FlexiCoder

is ideal for use

with either BIOS-compatible chip
sets or single-board computers for
PC systems requiring a custom
keyboard / keypad as an alternate
or additional input device. Boards
and evaluation kits are immediately
obtainable and ready to connect.

APPLICATIONS

PIN ASSIGNMENTS

FUNCTIONAL DESCRIPTION

PIN DEFINITIONS

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Mnemonic

DIP

PLCC

QFP

TYPE

Name and Function

Vcc

Power Supply: +5V

Vss

Ground

OSCI

Oscilator Input

OSCO

Oscilator Output

_RESET

Reset: apply 0 V to provide orderly
start-up.

_IRQ

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.

I/O

Keyboard Clock: connects to PC's
keyboard port Clock Line.

I/O

Keyboard Data: connects to PC's
keyboard port Data Line.

EKD

I/O

External Keyboard Data:
connects to external keyboard Data
Line.

EKC

I/O

External Keyboard Clock:
connects to external keyboard Clock
Line.

EKC1

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

Column Select Outputs: select

one of columns.

19-21

C8-C15

28-21

31-24

26-18

C16

C17

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

Row data inputs

38, 3

16, 33

No Connects: these pins are

18, 23

22, 39

unused.

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

The FlexiCoder

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 �S 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.

REPEAT KEYS

FUNCTIONAL DESCRIPTION, (CON'T)

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In custom masks, each key can be
defined individually to be either
Typematic or Single-Touch Action.
In the standard mask, all keys are
defined to be Single-Touch Action,
except the Arrow Keys. Pin RP
controls the repeat action of keys
that are defined to be Typematic.

Table 1: Typematic Action Control

The Typematic rate can be
controlled by issuing the
appropriate commands from the
system.

Repeat Mode

No repeat action

Repeat action

Switch Matrix Encoding

Each matrix location is programmed to represent either a single key or a
combination of keys of the IBM-standard 101/102 keyboard.

Scan Code Table Sets

The FlexiCoder

supports two scan code table sets. Scan Code Sets 1 and

2 are the default sets for PC/XT and AT/PS/2 systems respectively. For
more information, refer to the IBM Technical Reference Manual. Custom
scan code tables, including macros, are also available. Operating modes
are defined by the logic level of the relevant mode pins in the Mode Control
Unit.

Scan Matrix Data Integrity

The FlexiCoder

maintains the integrity of the codes corresponding to the

scanned matrix locations, independently of the Shift Status of the external
keyboard or the system. For example, if a key has been defined on the
matrix to send code corresponding to lower case letter "a", it will still send
the scan code for "a" even if the Shift Key has been pressed or the Caps
Lock has been set by the external keyboard. This is accomplished by
internally maintaining a set of flags to monitor the Shift Status of the external
keyboard and the system. If, for instance, the lower case key "a" is found to
be pressed and Caps Lock is set, the codes sent will be as follows:

1. Caps Lock Make Code

2. Caps Lock Break (this will reset the Caps Lock status of the system)

3. "a" Make Code

4. "a" Break Code

5. Lock Make Code

6. Caps Lock Break Code (this will restore the Caps Lock status of the
system)

SPECIAL HANDLING

SPECIAL HANDLING, (CON'T)

External Keyboard Connection

If an external keyboard was not
connected during power-on and
then connected at a later time, the
controller will proceed with the
normal reset routine in order to
initialize the external keyboard
properly. Thereafter, the
FlexiCoder

checks for the

presence of an external keyboard
every 2 seconds. After
communication has been
established, the controller continues
checking for the external
keyboard's presence. Should the
external keyboard be removed at a
later time, the K25C81 detects the
disconnection and will reinitiate the
reset sequence upon reconnection.
This feature allows the user to
connect and disconnect an external
keyboard at any time without
resetting the system.

EXT. KBD COMMUNICATION

MODE CONTROL

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The external keyboard
communication port of the
FlexiCoder

fully emulates a

standard 8042, available to an
83/101/102 external keyboard or
other compatible device.
Communication with an external
keyboard is accomplished via EKC
and EKD, Clock and Data lines
respectively. A third pin, EKC1
which connects to the Clock Line,
interrupts the controller whenever
an external keyboard initiates a
communication.

When power is first applied, the
controller proceeds with the
standard reset sequence with the
external keyboard. Data and
commands coming from the
external keyboard are buffered in
the controller's FIFO, along with
data from the scanned matrix, and
then presented to the system as if
originating from a single source.
Commands and data from the
system, after being acknowledged,
are then transmitted to the external
keyboard.

The FlexiCoder

implements all the

standard functions of
communication with a BIOS-
compatible PC/XT or AT/PS/2 host
system. Two lines, KC and KD,
provide bi-directional clock and
data signals according to the
protocol (PC or AT) selected. In
addition, the K25C81 supports
commands from and to the system,
as described in the IBM Technical
Reference Manuals. The following
table shows the commands that the
system may send and their value in
hex.

Command

Hex Value

Set/Reset Status

Indicators

Echo

Invalid Command

Select Alternate

Scan Codes

Invalid Command

Read ID

Set Typematic

Rate/Delay

Enable

Default Disable

Set Default

Set All Keys

Typematic

Make/Break

Make

Typematic/Make/Break

Set Key Type

Typematic

Make/Break

Make

Resend

Reset

Table 2: Keyboard Commands from the

System (AT/PS/2 protocol)

These commands are supported in
the AT/PS/2 protocol and can be
sent to the keyboard at any time.
Mode 1 accepts only the `reset'
command. Commands shown in
italics do not affect the operation of
the K25C81. Nevertheless, they
are acknowledged and relayed to
the external keyboard, if an
external standard keyboard is
present.

The following table shows the
commands that the keyboard may
send to the system.

Command

Hex Value

Key Detection

00*

Error/Overrun

Keyboard ID

83AB

BAT Completion Code

BAT Failure Code

Echo

Acknowledge (Ack)

Resend

Key Detection
Error/Overrun

FF*

*Scan Code Set 2

Table 3: Keyboard Commands to the

System (AT/PS/2 protocol)

When an external keyboard is
connected, commands from the
system will also be directed to the
external keyboard. Presence or
absence of an external keyboard
will not affect the normal operation
of the FlexiCoder

Электронный компонент: K25C81