Receiving Data From The Keyboard; Scan Code Translation - IBM 5170 Technical Reference

Receiving Data from the Keyboard
The keyboard sends data in a serial format using an II-bit frame.
The first bit is a start bit, and is followed by eight data bits, an
odd parity bit, and a stop bit. Data sent is synchronized by a
clock supplied by the keyboard. At the end of a transmission, the
keyboard controller disables the interface until the system accepts ,,-.....
the byte.
If
the byte of data is received with a parity error, a
Resend command is automatically sent to the keyboard. If the
keyboard controller is unable to receive the data correctly, a hex
FF is placed in its output buffer, and the parity bit in the status
register is set to I, indicating a .receive parity error. The keyboard
controller will also time a byte of data from the keyboard. If a
keyboard transmission does not end within two milliseconds, a
hex FF is placed in the keyboard controller's output buffer, and
the receive time-out bit in the status register is set. No retries will
be attempted on a receive time-out error.
Scan Code Translation
Scan codes, which are received from the keyboard, are converted
by the keyboard controller before they are put into the
~
controller's output buffer. The following figure shows the
keyboard layout with key numbers.
1-32 System Board