Texas Instruments 4000M - Manual (Page 102)

not display satisfactorily at lower values, so experiment
with your particular application. This has no effect on color
units.
I/O (Input/Output) Ports
You can individually disable the parallel or serial ports, if
not in use, to save battery power.
LCD Brightness Control
The LCD is a major power user in the computer. Reducing
the LCD brightness control level even a small amount
significantly reduces power usage. Always set the
brightness control to the lowest comfortable brightness
level, especially in low light conditions (for example, on an
airliner where longer battery charge life is important).
Optimizing Battery Operation
Power-Saving Utilities 5-9