Commands To The System; Resend (Hex Fe) - IBM AT 5170 Technical Reference

A Set/Reset Mode Indicators command consists of two bytes.
The first is the command byte and has the following bit setup:
11101101 - hex ED
The second byte is an option byte. It has a list of the indicators to
be acted upon. The bit assignments for this option byte are as
follows:
Bit Indicator
0
Scro 11 Lock Indicator
1
Num Lock Indicator
2
3-7
Caps Lock Indicator
Reserved (must be O's)
Note: Bit 7 is the most-significant bit; bit 0 is the
least-significant.
The keyboard will respond to the Set/Reset Mode Indicators
command with an ACK, discontinue scanning, and wait for the
option byte. The keyboard
will
respond to the option byte with
an ACK, set the indicators, and continue scanning if the keyboard
was previously enabled. If another command is received in place
of the option byte, execution of the function of the Set/Reset
Mode Indicators command is stopped with no change to the
indicator states, and the new command is processed. Then
scanning is resumed.
Commands to the
System
The commands described here are those sent by the keyboard.
They have a different meaning when issued by the system.
Resend (Hex FE)
The keyboard issues a Resend command following receipt of an
invalid input, or any input with incorrect parity. If the system
sends nothing to the keyboard, no response is required.
Keyboard 4-9