User Guide

CCS Technical Documentation 2 - System Module
RH-26
Issue 1 02/04 ©Nokia Corporation Page 29
Engine qwerty keypad LEDs are driven in 2 serial mode with each branch having its own
current limiting resistor. Serial resistance R is used to limit the current through the LEDs.
The feedback signal, FB, from LCD LEDs controls also the current of keypad LEDs. Qwerty
LEDs are controlled through UEMK CALLED1 pin.
Driver is controlled by the UEMK via DLight output. This signal is connected to driver EN-
pin (on/off).
Figure 10: Engine board LCD and keyboard LED connections
On the flip module, there is a transistor based “constant current” circuitry for LED driv-
ing. A diode is used to set the reference voltage, and resistors, Rs, are used to set the cur-
rent through transistor and LEDs.
LED drivers are controlled by the MCU I/O-pins. By setting either (qwerty & T9) of the
control signals “high”, the driver is enabled for the selected keypad.
Figure 11: Flip LED driver circuitry