HT82K628 Holtek Semiconductor Inc, HT82K628 Datasheet - Page 8

• Manufacturer Part Number: HT82K628
• Description: Windows 2000 Keyboard Encoder
• Manufacturer: Holtek Semiconductor Inc

·
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.
¨
¨
¨
¨
¨
The system overrides the clock line for at
least 60ms.
The keyboard checks the clock line state at
intervals of 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.
Preliminary
8
Data stream
Note: The parity bit is either 1 or 0, and the 8
b10:
b11:
B1:
B2:
b3:
b4:
b5:
b7:
b8:
b9:
data bits, plus the parity bit, always
have an odd number of 1ms.
B6
Mode 1,2,3
data bit 0
data bit 1
data bit 2
data bit 3
data bit 4
data bit 5
data bit 6
data bit 7
parity bit
(odd par)
always 0
always 1
start bit
stop bit
HT82K628A
July 20, 2000