User manual

ZEUS user manual
Issue E
44
LCD backlight brightness control
GPIO16 of the PXA270 processor is used for backlight brightness control (signal PWM0
on the J14 connector). The control of the backlight brightness is dependent upon the type
of backlight inverter used with the display. Some inverters have a ‘DIM’ function, which
uses a logic level to choose between two levels of intensity. If this is the case then
GPIO16 (Alternative Function 0) is used to set this. Other inverters have an input suitable
for a pulse-width modulated signal or analogue voltage control. In this case GPIO16
should be configured as PWM0 (Alternative Function 2).
Signal PWM0 is also routed through a low-pass filter on the ZEUS to enable analogue
voltage control of backlight brightness (signal BRT_CTRL on connector J24 – Backlight
power
- see page 84). The voltage range of BRT_CTRL is 0-2.5V.
STN bias voltage
The ZEUS provides a negative and a positive bias voltage for STN type displays (turned
on by the PXA270 GPIO101 pin). The negative and positive bias voltages are factory set
to -22V and +22V respectively. Pin connections for these can be found in the section J14
– LCD connector
, page 77. Please contact Eurotech Technical Support (see page 125)
for details of other bias voltages.
Do not exceed 20mA load current.
LVDS interface
There is an optional Low-Voltage Differential Signalling (LVDS) interface available on the
ZEUS. LVDS combines high data rates with low power consumption. The benefits of
LVDS include low-voltage power supply compatibility, low noise generation, high noise
rejection and robust transmission signals.
The National Semiconductor transmitter DS90C363 is used to convert 16-bits of LCD
data signals into three LVDS data streams. A phase-locked transmit clock is transmitted
in parallel with the data streams over a fourth LVDS link. The LVDS signals are routed to
the connector J16. For the connector details see the section J16 – LVDS connector
, page
78
.
The LVDS transmitter is enabled using the signal LVDS_EN (GPIO21 on PXA270).
Details are shown in the following table:
LVDS_EN
(CPU_GPIO 21) Selected LVDS function
0 LVDS power down (default)
1 LVDS enable