Theory of Operation: Controller 3-45
Prior to the LCD interpreting any commands, the correct display power-up sequence must be
initiated. First the V_EXT_1.85 (1.875 V) and V_2.775D (2.775 V) supplies must be at 90% or above
threshold and stable for 10us, and then reset can be asserted high. After OMAP de-asserts the reset
out signal (OMAP_RESET) the SLPOUT command can be sent. Now configuration commands are
ready to be sent to the LCD module.
The QVGA LCD module is only intended to operate up to +80°C due to ghosting effects. Therefore
software will shut off the display and backlight if the +80°C limit is reached. The display and backlight
will remain off until temperature drops below +75°C. The temperature sensor, U6401, for the display
cut-off is input into MAKO A/D Channel 3, pin M14.
For enhanced display readability, the default backlight is set to a dim state while the radio is in
Standby mode; however, the backlight turns to full brightness through a button press, call receive,
emergency call, and other status indicators. See Section 3.2.6.3: "Intelligent Lighting" for the display
backlight operation.
3.2.6.3 Intelligent Lighting
The APX 2000/ APX 4000/ APX 4000Li/ APX 1000 (900 MHz) radio is equipped with numerous
LEDs to provide intelligent lighting features. The Main board consists of a backlighting driver, which
illuminate all the LEDs throughout the radio, as shown in Figure 3-35. The backlighting driver,
U2201, provides white illumination to the main QVGA color display, Tricolor TX/RX indicator, status
indicator and white keypad backlights. The driver are controlled through OMAPs I2C interface (SCL
and SDA). The I2C communication protocol allows the OMAP chip to enable, disable, and control
the brightness of each LED. The driver uses PWM output to control the dimming modes operation. A
reset line issued by OMAP, OMAP_RESET, can be used to reset the driver. Some of the intelligent
lighting color schemes are shown in Table 3-6. The driver and LEDs are powered by Switcher 5
(V_SW_5).
Table 3-6. Color Schemes
Color
Default White
Out of Range Red
Low Battery Red
Emergency Amber
Call Received Green
Call Paged Green
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