User manual

Display Expansion Board - User’s Guide
Page 10
Copyright 2012 © Embedded Artists AB
There is also provision for mounting a programmable spread spectrum oscillator, DS1086LU+ from
Maxim, U21. It can be controlled via I2C.
Spread spectrum oscillators are used in order to comply with EMI emission requirements. It works fine
with the digital transmission interfaces but is does not work for the analog interface (VGA). In order for
the analog interface to work a fixed frequency oscillator is needed, typically 25.175 or 25.2 MHz for a
VGA signals. Note that this will likely compromise the emission levels and makes the CE marking of
the board void. It should only be done in a lab environment.
4.2.2 Page 3
The resistive touch screen controller, TSC2046 from Texas Instruments, is connected to the SPI bus.
See datasheet for details about its operation. There is ESD protection on the wires to the touch screen
since these are subject to possible electrostatic discharges from the user. This interface is typically not
used since most TV screens do not have a resistive touch screen interface.
There is further an I2C port expander, PCA9532 from NXP, which generate some control signals. In
addition it controls the selected oscillator (on page 2 of the schematic).
There is also an I2C-E2PROM that contains configuration information. For details see section 0. The
controller that generates the display signals can read the configuration information and easily
configures the LCD controller according to the information found. The memory shall only be read,
never written. The WP (Write Protect) signal is controlled from the I2C port expander and shall always
be high.
4.2.3 Page 4
The analog display interface (VGA) is based around the chip ADV7125KST50 from Analog Devices.
Read the datasheet for the chip for details.
Note that the I2C interface of the VGA connector is not connected. But it can be, as an experiment to
read information from the connected display.
4.2.4 Page 5
The LVDS interface is based around the chip DS90C383BMT from National Semiconductor/TI. Read
the datasheet for the chip for details. The LVDS signals can be accessed via a 2x10 pos, 100 mil pitch
pin list or via a 1.0mm pitch connector (mates with for example DF19G-20S-1C from Hirose).
There is a voltage switch for controlling an external LCD. The voltage can be 3.3V or 5V, selectable via
jumper JP7.
4.2.5 Page 6
The first HDMI/DVI interface is based around the chip TFP410 from TI. Read the datasheet for the chip
for details. The chips must be initialized via the I2C interface. The HDMI and DVI connectors are in
parallel and there is ESD protection for the interface.
4.2.6 Page 7
The second HDMI/DVI interface is based around the chip TDA19988 from NXP. Read the datasheet
for the chip for details. The chips must be initialized via the I2C interface. The TDA19988 chip has
support for CEC and audio transmission. An I2S audio source can be connected to J9.
The HDMI and DVI connectors are in parallel and there is ESD protection for the interface.
4.3 Interface Connector Pinning
The table below lists the signals on the interface connector J1. All signals are inputs (to the Display
Expansion Board) except where noted.
The I2C interface is for controlling the HDMI/DVI transmitters as well as for communicating with the
e2prom that contains configuration information. It is also for communicating with the i2c port expander