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K25C81-P Datasheet

  • K25C81-P

  • Versatile PC/XC/AT/PS/2 Compatible Keyboard Encoder

  • 12頁

  • SEMTECH   SEMTECH

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EXT. KBD COMMUNICATION
The external keyboard
communication port of the
FlexiCoder
TM
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鈥檚 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.
MODE CONTROL
The FlexiCoder
TM
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
Set/Reset Status
Indicators
Echo
Invalid Command
Select Alternate
Scan Codes
Invalid Command
Read ID
Set Typematic
Rate/Delay
Enable
Default Disable
Set Default
Hex Value
ED
EE
EF
F0
F1
F2
F3
F4
F5
F6
F7
F8
F9
FA
FB
FC
FD
FE
FF
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 鈥榬eset鈥?/div>
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
Key Detection
Error/Overrun
Keyboard ID
BAT Completion Code
BAT Failure Code
Echo
Acknowledge (Ack)
Resend
Key Detection
Error/Overrun
Hex Value
00*
83AB
AA
FC
EE
FA
FE
FF*
*Scan Code Set 2
Table 3:
Keyboard Commands to the
System (AT/PS/2 protocol)
Set All Keys
Typematic
Make/Break
Make
Typematic/Make/Break
Set Key Type
Typematic
Make/Break
Make
Resend
Reset
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
TM
.
Table 2:
Keyboard Commands from the
System (AT/PS/2 protocol)
Copyright Semtech, 1997-2001
DOC5-C81-DS-105
5
www.semtech.com

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