eKK8011AB
USB & PS/2 Keyboard Encoder
6 Function Description
This section is divided into subsections for user convenience and clearer distinction.
Detailed PS/2 keyboard function descriptions are provided in Section 6.1. The USB
keyboard function descriptions are discussed in details in Section 6.2.
6.1 PS/2 Keyboard Function Description
The keyboard buffer, power-on reset and self test, input, output, commands, and scan
codes are described 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 receives
scan codes from the keyboard. The response codes and repeated codes will not be
buffered. If the 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 of 300
milliseconds and a maximum of 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 ms to 2.5 s after POR,
and between 300 ms to 500 ms 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 the 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 is 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 buffers the data and return the clock and data lines to a high state.
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Product Specification (V1.4) 07.10.2006
(This specification is subject to change without further notice)
ELAN [ ELAN MICROELECTRONICS CORP ]
