eKK8011AB
USB and PS/2 Keyboard Encoder
6.1.4 Keyboard Data Input
When the system is ready to send data to the keyboard, it first checks the clock line to
see if keyboard is sending data. If keyboard is not sending data or it is sending data but
has not reached the 10th clock, the system can inhibit the interface by forcing the clock
line low for more than 60 microseconds and prepares to send data. The keyboard
checks the clock line status at least every 5 milliseconds. If a system Request to Send
(RTS) is detected, the keyboard clocks 11 bits in. After the 10th bit, the keyboard
checks for a high state in the data line then pulls it low and clocks one more bit to signal
the system that data has been received. If data is low after the 10th bit, it indicates a
frame error. The keyboard should continue to count until the data line goes high, then
pulls it low and issues a RESEND to the system.
6.1.5 Command from the System
The system can send commands to the keyboard at any time. The keyboard needs to
respond within 20 milliseconds, unless the system prevents keyboard output, when
doing self test or executing a reset. The following are the keyboard input commands
and the actions that the keyboard needs to take.
Set /Reset Status indicators (Hex ED)
- Responds with ACK
- Receives option byte
- Responds with ACK
- Updates status indicators
- Returns to previous scanning state
Echo (Hex EEH)
- Responds with EE hex
- Returns to previous scanning state
Invalid commands (Hex EF and F1)
- Returns a RESEND command
- Returns to previous scanning state
Select Alternate Scan Codes (Hex F0)
- Responds ACK
- Clears output buffer
- Sets the default Typematic rate/delay
- Clears last Typematic key
- Receives option byte
- Responds ACK
- Option byte : 01 : selects scan code Set 1
02 : selects scan code Set 2
03 : selects scan code Set 3
- Returns to previous scanning rate
Product Specification (V1.4) 07.10.2006
(This specification is subject to change without further notice)
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ELAN [ ELAN MICROELECTRONICS CORP ]
