K25C81-FB Datasheet, PDF (5/12 Pages) Semtech Corporation – Versatile PC/XC/AT/PS/2 Compatible Keyboard Encoder

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’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.
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
Hex Value
Set/Reset Status
ED
Indicators
Echo
EE
Invalid Command
EF
Select Alternate
F0
Scan Codes
Invalid Command
F1
Read ID
F2
Set Typematic
F3
Rate/Delay
Enable
F4
Default Disable
F5
Set Default
F6
Set All Keys
Typematic
F7
Make/Break
F8
Make
F9
Typematic/Make/Break FA
Set Key Type
Typematic
FB
Make/Break
FC
Make
FD
Resend
FE
Reset
FF
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
AA
BAT Failure Code
FC
Echo
EE
Acknowledge (Ack)
FA
Resend
FE
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^TM.
Copyright Semtech, 1997-2001
5
DOC5-C81-DS-105
www.semtech.com