Illumination - Nokia RH-37 Series Manual

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When there is no key pressed, all the inputs from the rows are high since UPP has inter-
nal pull-up resistors on all those lines. All the columns are low at this state. When a key
is pressed, the specific row where the key is placed is pulled low. This generates an inter-
rupt to the MCU and the MCU now starts its scanning procedure. The procedure first sets
all the columns high (KEYB (1) to KEYB (4)) and then one by one low again. Only one of
the columns is low at the time. While one of the columns is low, the row is (KEYB (5) to
KEYB (9)) is read by MCU to find the active low signal. If the input is low, the MCU knows
that a key is pressed. When the key has been detected all the keypad-register inside the
UPP is reset and it's ready receiving new interrupt.
The power on key is connected to the UEM PWRONX signal.

Illumination

In RH-37, white LED's are used for the LCD backlight and keypad lighting. Three LED's are
used for the LCD lighting and two LED's for the keyboard. A step up DC-DC converter is
used as a LED driver that is configured as a constant current source.
Issue 1 07/04
Figure 13: RH-37 keypad
©Nokia Corporation
RH-37
System Module
Page 33