ht82k628a Holtek Semiconductor Inc., ht82k628a Datasheet - Page 5

• Manufacturer Part Number: ht82k628a
• Description: Ht82k628a -- Windows 2000 Ps/2 Keyboard Encoder
• Manufacturer: Holtek Semiconductor Inc.

FEH - Resend
The host sends this command when it detects an error in
any transmission from the HT82K628A. It is sent only af-
ter a data transmission and before the host allows the
next data output. When a Resend is received, the
HT82K628A sends the previous output again (unless
the previous output was Resend, in which case the
HT82K628A sends the last byte before the Resend
command).
Commands to the Host
The following table shows the commands that the
HT82K628A may send to the host, and their hexadeci-
mal values.
00H or FFH - Key Detection Error
The HT82K628A sends a key detection error character if
conditions in the keyboard make it impossible to identify
a switch closure. If the HT82K628A is using scan code
set 1, the code is FFH. For sets 2 and 3, the code is 00H.
00H or FFH - Overrun
An overrun character is placed in the HT82K628A buffer
and replaces the last code when the buffer capacity has
been exceeded. The code is sent to the host when it
reaches the top of the buffer queue. If the HT82K628A is
using scan code set 1, the code is FFH. For sets 2 and 3,
the code is 00H.
83AbH - Keyboard ID
The keyboard ID consists of 2 bytes, Hex 83AbH. The
HT82K628A responds to the Read ID with ACK, discon-
tinues scanning and sends 2 ID bytes. The low byte is
sent first followed by the high byte. Following the output
of Keyboard ID, the HT82K628A begins scanning.
EEH - Echo
The HT82K628A sends this code in response to an
Echo command.
Rev. 1.60
Key Detection Error/Overrun 00 (Code Set 2 and 3)
Keyboard ID
Bat Completion Code
Bat Failure Core
Echo
Acknowledge
Resend
Key Detection Error/Overrun
Command
FF (Code Set 1)
Hex Value
83AB
AA
FC
EE
FA
FE
5
AAH - BAT Completion Code
Following satisfactory completion of the BAT, the
HT82K628A sends AAH. Any other code indicates key-
board failure.
FCH - BAT Failure Code
If a BAT failure occurs, the HT82K628A sends this code,
discontinues scanning and waits for a host response or
reset.
FEH - Resend
The HT82K628A issues a Resend command following
receipt of an invalid input or any input with incorrect par-
ity. If the host sends nothing to the HT82K628A, no re-
sponse is required.
Data Communications
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 continues to count until the data
line becomes active. The keyboard then makes the
data line inactive and sends a Resend.
If CLK=0, no transmission (keyboard is inhibited).
If CLK=1, DATA=0, no transmission (system re-
quest to send).
If CLK=1, DATA=1, transmission permitted.
Data will be valid before the trailing edge and be-
yond the leading edge of the clock.
The KB checks the clock line for an active level of 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 clock line state at inter-
vals of 10ms
If a system request-to-send is detected, the key-
board 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
reception of this signal, the system returns
keyboard has received its data. Upon
to the ready state, in which it can accept
keyboard outputs or goes to the inhibit
state until it is ready.
HT82K628A
April 16, 2004