HT82K28A(2000) View Datasheet(PDF) - Holtek Semiconductor

Part Name

Description

Manufacturer

HT82K28A
(Rev.:2000)

Win98 Keyboard Encoder

Holtek Semiconductor 

Functional Description

The HT82K28A basic function is to detect key

press and release activity and to transmit the

corresponding scan code, as well as make and

break codes to the system.

The device also accepts commands from the sys-

tem and responds to the system if necessary. All

communication between the keyboard and the

system is managed through the CLOCK and

DATA pins.

The keyboard begins to scan for pressed or re-

leased keys and commands from the system after

the BAT (Basic Assurance Test) has been run.

Working modes

Three working modes are supported by the

HT82K28A. These are setup by the alternate

scan code command F0. The various modes are

described as follows.

Mode 1

· Supports code set 1 for PS/2 model 30 key-

boards.

· Enters mode1 after an F0 Command is issued

followed by a 1".

· Contains an 11 bit data stream, including one

start bit (always zero) eight data bits, one par-

ity bit (odd parity) and one stop bit (always

one).

· All keys are typematic/make/break as default.

· The working mode can be changed again in

this mode, by issuing an F0 command fol-

lowed by an option. See the F0 command for

more detail.

Mode 2

· Supports code set 2 for PC/AT, PS/2 model 50,

60 keyboards.

· Enters mode 2 after power on.

The working mode can be changed by an F0

command followed by an option byte 1, 2 or 3.

See the F0 command for more details.

· Contains an 11 bit data stream, including one

start bit (always zero) eight data bits, one par-

ity bit (odd parity) and one stop bit (always

one)

· All keys are typematic/make/break as default.

HT82K28A

Mode 3

· Supports code set 3, for PS/2 model 80 key-

boards.

· Enters mode 3 when an F0 command is issued

followed by a 3".

· Contains an 11 bit data stream, including one

start bit (always zero) eight data bits, one par-

ity bit (odd parity) and one stop bit (always

one).

Buffers

The buffers support the following functions:

· 16-byte FIFO buffer: stores 16 keystrokes

scan codes.

· Additional keystrokes will be ignored.

· Response codes, i.e FA/FE... do not occupy

buffer positions.

Basic assurance test - BAT

The following functions are offered by the Basic

Assurance Test:

· Turns on LED status indicators.

· Keyboard processor test.

· RAM test.

· Turns off LED status indicators, i.e. the

LEDs.

· Reports the BAT result to the system.

Note: During the BAT, activity on the "clock"

and "data" line are ignored. The LED¢s

are turned on at the beginning and

turned off at the end of the BAT. The

BAT takes a minimum of 450ms after

POR and a maximum of 2.5s. The re-

sponse to a satisfactory BAT completion

is ²AA² and response to BAT failure is

an ²FC² error. The reset keyboard com-

mand ²FF² will also cause the keyboard

to execute the BAT. Completion codes

are sent between 300 and 500ms after a

reset command is acknowledged. After

the BAT, the keyboard sets the keys to

typematic and make/break, and sets the

default typematic rate and delay.

4

February 16, 2000

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