HT82K28 Holtek Semiconductor Inc, HT82K28 Datasheet - Page 8

• Manufacturer Part Number: HT82K28
• Description: Win98 Keyboard Encoder
• Manufacturer: Holtek Semiconductor Inc

·
Commands to the system
00: keyboard detect a error/overrun (set 2, set 3)
AB,83: keyboard ID
AA: BAT completion
FC: BAT failure
EE: Echo
FA: Acknowledge
FE: Resend
FF: Keyboard detects a overrun (set 1)
·
·
Default
FA: Acknowledge
If the KB (Keyboard) receives any valid input
except EE (echo) and resend (FE) then send
an FA to the system first.
If the command is EE, then send an EE back
to the system.
If the command is FE, then send the last key
code to system.
If there is an interrupt while sending FA, the
KB discards the FA and accepts the command
from the system and processes it.
00/FF: Key overrun
If the keyboard detects an overrun error, the
KB sends an overrun error code to the system.
mode 1: FF
mode 2,3: 00
b4~b0
¨
¨
00000
00001
00010
00011
00100
00101
00110
00111
01000
01001
01010
01011
01100
01101
01110
01111
delay: 500ms± 20%
typematic rate=10.9 characters/sec± 20%
Typematic
rate
30.0
26.7
24.0
21.8
20.0
18.5
17.1
16.0
15.0
13.3
12.0
10.9
10.0
9.2
8.6
8.0
b4~b0
10000
10001
10010
10011
10100
10101
10110
10111
11000
11001
11010
11011
11100
11101
11110
11111
Typematic
rate
7.5
6.7
6.0
5.5
5.0
4.6
4.3
4.0
3.7
3.3
3.0
2.7
2.5
2.3
2.1
2.0
8
·
Data communications
·
·
FE: Resend
The KB issues an FE when there is a parity
error in transmission.
Data output
Data input
If the keyboard "data" line is found to be at an
inactive level following the 10th bit, a frame
error has occurred, and the keyboard contin-
ues to count until the "data" line becomes ac-
tive. The keyboard then makes the "data" line
inactive and sends a Resend.
¨
¨
¨
¨
¨
¨
¨
¨
¨
¨
¨
If CLK=0, no transmission (keyboard inhib-
ited).
If CLK=1, DATA=0, no transmission (sys-
tem request to send).
If CLK=1, DATA=1, transmission permit-
ted.
Data will be valid before the trailing edge
and beyond the leading edge of the clock.
The KB checks the clock line for an active
level at least every 60ms.
If line contention occurs (system brings the
clock low before the tenth clock), set
clock=data=high.
The system overrides the clock line for at
least 60ms
The keyboard checks the state of the clock
line at intervals of no more than 10ms
If a system request-to-send is detected, the
keyboard counts 11 data bits.
Data will be valid before the rising edge and
beyond the falling edge
After the 10th bit, the keyboard checks for
an active level on the "data" line. If the line
is active it is forced to be inactive, and
counts one more bit.
Note: This action signals the system that
the keyboard has received its data.
Upon reception of this signal, the
system returns to the ready state, in
which it can accept keyboard outputs
or goes to the inhibit state until it is
ready.
February 16, 2000
HT82K28A