Nokia 8390 Manuales De Servicio
NSB-8
System Module & UI
PAMS Technical Documentation
Page 36
ãNokia Corporation
Issue 1 01/02
UI Board LK5
NSB-8 consists of separate UI board, named as LK5, which includes contacts for the key-
pad domes and LEDs for keypad illumination. UI board is connected to main PWB
through 16 pole board-to-board connector with springs. Signals of the connector are
described in section External and Internal Signals and Connections.
pad domes and LEDs for keypad illumination. UI board is connected to main PWB
through 16 pole board-to-board connector with springs. Signals of the connector are
described in section External and Internal Signals and Connections.
5x4 matrix keyboard is used in NSB-8. Key pressing is detected by scanning procedure.
Keypad signals are connected UPP keyboard interface.
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 interrupt MCU starts scanning procedure. All columns
are first written high and then one column at the time is written down. All other col-
umns 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 detecting pressed key all reg-
isters inside the UPP are reset and columns are written back to zero.
columns are written zero. When key is pressed one row is pulled down and an interrupt is
generated to MCU. After receiving interrupt MCU starts scanning procedure. All columns
are first written high and then one column at the time is written down. All other col-
umns 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 detecting pressed key all reg-
isters inside the UPP are reset and columns are written back to zero.
LCD & Keypad Illumination
In NSB-8 white LEDs are used for LCD and keypad illumination. For LCD illumination four
LEDs (on RM8) are used and for keypad six LEDs (on LK5).
LEDs (on RM8) are used and for keypad six LEDs (on LK5).
Current through LEDs is controlled by transistor circuitry. External transistor driver cir-
cuitry is used as constant current source in order to prevent any change in battery volt-
age be seen as changing led brightness. Battery voltage is changing, for example, during
charging.
cuitry is used as constant current source in order to prevent any change in battery volt-
age be seen as changing led brightness. Battery voltage is changing, for example, during
charging.
Figure 9: Display and keypad illumination circuitry.
LEDs are controlled by the UEM PWM outputs. Both LED groups are controlled by KLight
output of the UEM. Current flow through the LEDs is set by biasing the transistor and
limiting the current by resistors. Current is set separately to keypad and LCD LEDs.
output of the UEM. Current flow through the LEDs is set by biasing the transistor and
limiting the current by resistors. Current is set separately to keypad and LCD LEDs.
KLIGHT
Display
LEDs
LEDs
Keypad
LEDs
VBAT
15R
10R
470R