ht82k628a Holtek Semiconductor Inc., ht82k628a Datasheet - Page 3

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

Functional Description
Command from the Host
The following table shows the commands that the host
may send and their hexadecimal values.
The commands may be sent to the HT82K628A at any
time and the HT82K628A will respond within 25ms ex-
cept when performing the internal diagnostics or execut-
ing a Reset command.
EDH - Set/Reset Status Indicators
Three status indicators on the keyboard-Num Lock,
Caps Lock, and Scroll Lock-are accessible by the host.
The HT82K628A activates or deactivates these indica-
tors when it receives a valid command-code sequence
from the system. The command sequence begins with
the command byte (hex ED). The HT82K628A responds
to the command byte with ACK, discontinues scanning,
assignments for this option byte are as follow:
If a bit for an indicator is set to 1, the indicator is turned
on. If a bit is set to 0, the indicator is turned off.
Rev. 1.60
Set/Reset Status Indicators
Echo
Invalid Command
Select Alternate Scan Codes
Invalid Command
Read ID
Set Typematic Rate/Delay
Enable
Default Disable
Set Default
Set All Keys - Typematic
Set All Keys - Make/Break
Set All Keys - Make
Set All Keys - Typematic/Make/Break
Set Key Type - Typematic
Set Key Type - Make/Break
Set Key Type - Make
Resend
Reset
0
1
2
3~7
Bit
Scroll Lock Indicator
Num Lock Indicator
Caps Lock Indicator
Reserved (Must be 0)
Command
Indicator
Hex Value
ED
EE
FC
FD
EF
F0
F1
F2
F3
F4
F5
F6
F7
F8
F9
FA
FB
FE
FF
3
The HT82K628A responds to the option byte with ACK,
sets the indicators and if the HT82K628A was previously
enabled, continues scanning. The status of the indica-
tors will reflect the bits in the option byte and can be acti-
vated or deactivated in any combination. If another
command is received in place of the option byte, execu-
tion of the Set/Reset Mode Indicators command is
stopped, with no change to the indicator status, and the
new command is processed.
Immediately after power-on, the lights default to the off
state. If the Set Default and Default Disable commands
are received, the lamps remain in the state they were in
before the command was received.
EEH - Echo
Echo is a diagnostic aid. When the HT82K628A re-
ceives this command, it issues a hex EE response and if
the HT82K628A was previously enabled, continues
scanning.
EFH and F1H - Invalid Command
EFh and F1h are invalid commands and are not sup-
ported. If HT82K628A receives one of these and sends
it, the HT82K628A will not acknowledge the command,
but returns a Resend command and continues in its pre-
vious scanning state.
F0H - Select Alternate Scan Codes
This command instructs the HT82K628A to select one of
the three sets of scan codes. The HT82K628A acknowl-
edges receipt of this command with ACK, clears both
the output buffer and the typematic key. The host then
sends the option byte and the keyboard responds with
another ACK. An option byte value of hex 01 selects
scan code set 1, hex 02 selects set 2 and hex 03 selects
code set3.
An option byte value of hex 00 causes the HT82K628A
to acknowledge with ACK and sends a byte telling the
host which scan code set is currently in use.
After establishing the new scan code set, the
HT82K628A returns to the scanning state it was in be-
fore receiving the Select Alternate Scan Codes com-
mand.
F2H - Read ID
This command requests identification information from
the HT82K628A. The HT82K628A responds with ACK,
discontinues scanning and sends the two keyboard ID
bytes hex 83h and Abh. After the output of the second ID
byte, the HT82K628A resumes scanning.
HT82K628A
April 16, 2004