No-Operation (Nop) (Hex F2 Through Ef); Echo (Hex Ee); Set/Reset Mode Indicators (Hex Ed) - IBM 5170 Technical Reference

function ends with no change to the existing rate, and the new
command is processed. However, the keyboard will not resume
scanning unless instructed to do so by an Enable command.
The default rate for the system keyboard is as follows:
The typematic rate
=
10 characters per second ± 20% and the
delay = 500 ms ±20%.
No-Operation (NOP) (Hex F2 through EF)
These commands are reserved and are effectively no-operation
(NOP). The system does not use these codes.
If
sent, the
keyboard acknowledges the command and continues in its prior
scanning state. No other operation will occur.
Echo (Hex EE)
Echo is a diagnostic aide. When the keyboard receives this
command, it issues a hex EE response and continues scanning if
the keyboard was previously enabled.
Set/Reset Mode Indicators (Hex ED)
Three mode indicators on the keyboard are accessible to the
system. The keyboard activates or deactivates these indicators
when it receives a valid command from the system. They can be
activated or deactivated in any combination.
It
is up to the using system to remember the previous state of an
indicator. This is in case its setting does not change when a
command sequence is issued to change the state of another
indicator.
The system remembers the previous state of an indicator so that
its setting does not change when a command sequence is issued to
~
change the state of another indicator.
The command has the following format:
4-8 Keyboard