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6.5 Backlight Control
This terminal has incorporated two types of automatic backlight control functions: ABO (Auto
Backlight OFF) and ABC (Auto Backlight Control). The ABO function is used to turn off the
backlight if no key or touch panel input has been made for a given period of time, and the ABC
function is used to automatically turn on and off the backlight depending on the intensity of the
ambient light. These operations are performed by the keyboard controller.
ABC (Auto Backlight Control)
The ABC function automatically turns on or off the backlight by detecting the ambient light
intensity. Every second it determines the amount of light received by the illumination sensor and
automatically turns on or off the backlight depending on whether the amount of light is less than the
given amount or more than the given amount.
Fig. 6.5
In the above graph, the marginal light amount across which the backlight is turned ON is at a setting
less than if the backlight is OFF. If these two levels are identical, the backlight will flicker if it
detects a small variation in the incident light on the illumination sensor. To avoid this problem an
appropriate hysterisis is provided.
Amount of Light
Dark
Light
Margin to
turn ON
Margin to
turn OFF
Backlight OFF
Backlight ON
