eKK8011
USB & PS/2 Keyboard Encoder
6 Function Description
The PS/2 keyboard function descriptions are provided in Section 6.1. In section 6.2,
we provide the USB keyboard function descriptions.
6.1 PS/2 Keyboard Function Description
We describe the keyboard buffer, power-on Reset and self test, input, output,
command, and scan codes in the following sections.
6.1.1 Keyboard Buffer
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.
6.1.2 Power-on Reset and Self Test
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.
6.1.3 Keyboard Data Output
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 10th clock, the keyboard should
stop sending, then buffer the data and return clock and data lines to high state.
6.1.4 Keyboard Data Input
When the system is ready to send data to the keyboard, it 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 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
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Product Specification (V1.0) 06.10.2003
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
