K25C81-FB Datasheet, PDF(4/12 Page) Semtech Corporation – Versatile PC/XC/AT/PS/2 Compatible Keyboard Encoder

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K25C81-FB Datasheet, PDF (4/12 Pages) Semtech Corporation – Versatile PC/XC/AT/PS/2 Compatible Keyboard Encoder

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REPEAT KEYS

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.

Repeat Mode

No repeat action

Repeat action

Table 1: Typematic Action Control

The Typematic rate can be

controlled by issuing the

appropriate commands from the

system.

SPECIAL HANDLING

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

FlexiCoderTM checks for the

presence of an external keyboard

every 2 seconds. After

communication has been

established, the controller continues

checking for the external

keyboardâs 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.

FUNCTIONAL DESCRIPTION, (CONâT)

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 FlexiCoderTM 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.

SPECIAL HANDLING, (CONâT)

Scan Matrix Data Integrity

The FlexiCoderTM 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 âaâ, it will still send

the scan code for âaâ 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 âaâ 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. âaâ Make Code

4. âaâ Break Code

5. Lock Make Code

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

system)

DOC5-C81-DS-105

www.semtech.com

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