User Guide

NPM–9
System Module & UI
PAMS Technical Documentation
Page 37
Issue 1 02/2002
 Nokia Corporation
UI Board LU9
NPM–9 consists of separate UI board, named as LU9, which includes
contacts for the keypad domes and LEDs for keypad illumination. UI
board is connected to main PWB through 16 pole board–to–board con-
nector with springs. Signals of the connector are described in section Ex-
ternal and Internal Signals and Connections.
5x4 matrix keyboard is used in NPM–9. Key pressing is detected by scan-
ning procedure. Keypad signals are connected UPP keyboard interface.
When no key is pressed row inputs are high due to UPP internal pull–up
resistors. The columns are written zero. When key is pressed one row is
pulled down and an interrupt is generated to MCU. After receiving inter-
rupt MCU starts scanning procedure. All columns are first written high and
then one column at the time is written down. All other columns except one
which was written down are set as inputs. Rows are read while column at
the time is written down. If some row is down it indicates that key which is
at the cross point of selected column and row was pressed. After detect-
ing pressed key all register inside the UPP are reset and columns are
written back to zero.
LCD & Keypad Illumination
In NPM–9 blue leds are used for LCD and keypad illumination. For LCD
illumination four leds are used and for keypad six leds.
Current through leds is controlled by transistor circuitry. External transis-
tor driver circuitry is used as constant current source in order to prevent
any change in battery voltage be seen as changing led brightness. Bat-
tery voltage is changing for example during charging depending on a
charger, battery type and age.
LCD leds
Keypad leds
KLight
VBATT
10R
VBATT
15R
VBATT
330R