User Guide

Technical Documentation
NHD–4
Uif Module
PAMS
Page 6–5
Original 11/97
Keyboard scanning and display driver control
COL(0–4) are used as column lines in keyboard. UIF(0–5) are used as
row lines. They are also multiplexed with display driver control signals.
When a key is pressed the ASIC gets an interrupt from a row and the
MCU starts scanning. One column at a time is written to low and rows are
used to read which key it was. The power off detection is multiplexed with
one row; when all keys on the row seems to be pressed the ASIC knows
that power key is pressed. The power key is also connected to PSL+ to
switch the power on.
Keyboard and display illumination
The keyboard illumination is achieved by using two transistors wired as
simple constant current sinks. Each transistor supplies eight leds. The
bases of the transistors are all wired together and supplied by emitter
follower V40. The led current is fixed by the values of R44 and R45 and
the ratio of R51 to R52.
The display illumination operates in a similar way to the keyboard drivers,
two transistors are used to drive eight LED’s. The current in this case is
defined by the value of R46, R47 and the ratio of R51 to R52.
The Call LED is fed from a simple emitter follower.
Audio Circuitry
The earpiece is routed directly via series resistors to connector X4. The
earpiece is dynamic type.
The microphone is of the electric type and needs a voltage supply for
operation. When MIC_ENA is low bias voltage is connected to the
microphone via transistor V8. V2 is wired as a switch for VA2, controlled
by the microphone enable line [MICENA].
The buzzer is a dynamic one and is driven from a two transistor switch
which acts as a buffer for a CMOS output signal applied at BUZZER. The
ringing volume is controlled by pulse width modulation.The diode V37
prevents damage to the transistor when switched off, absorbing the stored
energy in the buzzer inductance and suppressing large positive going
spikes on the transistor collectors.
LCD Module Interface
The LCD module includes the LCD and the display driver. The driver TAB
is connected with heat seal connection to the LCD. Viewing direction is 6
o‘clock. It has internal clock oscillator and negative voltage generator.
The display module is connected to the UIF module with 24 pin soldered
connection.