IBM 5251 Series Maintenance Information Manual page 181

KEYLOCK FEATURE
A Keylock feature is available on the display station for
security of data.
When the Keylock is in the locked position while the
Status switch is set to the Normal position, the display
screen is blank except for the system indicators on the
right side of the screen. Data displayed at the time the
Keylock is changed to the locked position is controlled
by the application program. Keyboard data entered
while the Keylock is in the locked position will not be
displayed by the display station.
The Keylock feature can be in either the locked or the
unlocked position, and the power-on diagnostic still
functions the same.
Keylock
Locked
- -
Unlocked
Features
I/O Control Microprocessing Unit
Features 5251 MIM 5-1