K25C81-FB Semtech, K25C81-FB Datasheet - Page 4

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

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.
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
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.
Copyright Semtech, 1997-2001
DOC5-C81-DS-105
REPEAT KEYS
SPECIAL HANDLING
Repeat Mode
No repeat action
Repeat action
TM
checks for the
RP
L
H
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
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
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)
FUNCTIONAL DESCRIPTION, (CON’T)
SPECIAL HANDLING, (CON’T)
4
TM
TM
supports two scan code table sets. Scan Code Sets 1 and
maintains the integrity of the codes corresponding to the
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