EKK8301 ELAN Microelectronics Corp, EKK8301 Datasheet - Page 8

• Manufacturer Part Number: EKK8301
• Description: Keyboard Encoder
• Manufacturer: ELAN Microelectronics Corp

eKK8301
Keyboard Encoder
6
4 •
Function Descriptions
6.1 Keyboard Buffer
6.2 Power-on Reset and Self Test
6.3 Keyboard Data Output
6.4 Keyboard Data Input
The keyboard will buffer 16 bytes in a first-in first-out order when the system is able to
receive scan codes from the keyboard. The response codes and repeated codes will
not be buffered. If keystrokes generate a multiple-byte sequence, the entire
sequence must fit into the buffer or the keystroke is discarded and a buffer-overrun
condition occurs.
The duration of the keyboard Power-on Reset(POR) should be within 150
milliseconds and 2 seconds after the power is applied to the keyboard.
After executing POR, the keyboard executes a self test. The LEDs are turned on at
the beginning and off at the end of the self test. The self test takes a minimum 300
milliseconds and a maximum 500 milliseconds. If the self test is successful, a
completion code AA hex is sent to the system and the keyboard starts scanning. If
the self test fails, and error code is sent, the keyboard is disabled and waits for a
command from the system. The completion codes are sent between 450
milliseconds and 2.5 seconds after POR, and between 300 and 500 milliseconds after
a RESET command is acknowledged.
When the keyboard is ready to send data to the system, it first checks clock and data
lines. If either one is in the low state, data is stored in the keyboard buffer. If both
are in the high state, keyboard starts clocking data out. Data will be valid before the
trailing edge and after the leading edge of the clock pulse. During the transmission
the keyboard checks the clock line at least every 60 microseconds. If the system
lowers the clock lines before the leading edge of the 10
stop sending, then buffer the data and return clock and data lines to high state.
When the system is ready to send data to the keyboard, if first checks 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 10
clock line low for more than 60 microseconds and prepares to send data. The
keyboard checks 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 10
keyboard checks for a high state in 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 10
indicates a frame error. The keyboard should continue to count until data line goes
high, then pulls it low and issues a RESEND to the system.
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clock, the system can inhibit the interface by forcing the
(This specification is subject to change without further notice)
Product Specification (V1.0) 08.07.2002
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