ht82k28a Holtek Semiconductor Inc., ht82k28a Datasheet - Page 3

• Manufacturer Part Number: ht82k28a
• Description: Ht82k28a -- Win98 Keyboard Encoder Restricted Products
• Manufacturer: Holtek Semiconductor Inc.

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 system
and responds to the system if necessary. All communi-
cation between the keyboard and the system is man-
aged through the CLOCK and DATA pins.
The keyboard begins to scan for pressed or released keys
and commands from the system after the BAT (Basic As-
surance 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
Mode 2
Mode 3
Buffers
The buffers support the following functions:
Rev. 1.30
Supports code set 1 for PS/2 model 30 keyboards.
Enters mode1 after an F0 Command is issued fol-
lowed by a 1 .
Contains an 11 bit data stream, including one start bit
(always zero) eight data bits, one parity 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 followed by an op-
tion. See the F0 command for more detail.
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 com-
mand 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 parity bit (odd parity)
and one stop bit (always one)
All keys are typematic/make/break as default.
Supports code set 3, for PS/2 model 80 keyboards.
Enters mode 3 when an F0 command is issued fol-
lowed by a 3 .
Contains an 11 bit data stream, including one start bit
(always zero) eight data bits, one parity bit (odd parity)
and one stop bit (always one).
16-byte FIFO buffer: stores 16 keystrokes scan codes.
Additional keystrokes will be ignored.
Response codes, i.e FA/FE... do not occupy buffer po-
sitions.
3
Basic assurance test - BAT
The following functions are offered by the Basic Assur-
ance Test:
Note:
Power-on
Two important activities take place when power is first
applied to the keyboard. The first is the presence of an
H/W signal POR (Power-On-Reset) that resets the key-
board processor. The second activity is the running of
the self test BAT (Basic Assurance Test) routine.
PC-type/mode/code set
The following table describes the relationship between
different computer types, the working mode and the
code sets.
The mode can be changed between mode 2 & 3.
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.
PS/2 30
PS/2 50
PS/2 60
PS/2 80
PC-AT
During the BAT, activity on the clock and
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
error. The reset keyboard command FF will
also cause the keyboard to execute the BAT.
Completion codes are sent between 300 and
500ms after a reset command is acknowl-
edged. After the BAT, the keyboard sets the
keys to typematic and make/break, and sets the
default typematic rate and delay.
data line are ignored. The LED s are turned
AA
and response to BAT failure is an FC
mode 1
mode 2
mode 2
mode 2
mode 3
HT82K28A
code set 1
code set 2
code set 2
code set 2
code set 3
June 27, 2002