User manual

LPC3250 Developer’s Kit v2 - User’s Guide
Page 61
Copyright 2013 © Embedded Artists AB
6 LCD Expansion Connector
Embedded Artists supplies many different display options as add-on boards. These display boards are
great to use for getting started quickly and test a specific display resolution in an application. All LCD
boards supplied from Embedded Artists use the LCD Expansion Connector. There is also an option to
connect custom displays via the LCD Expansion Connector, J26.
The OEM Base Board contains a buffered LCD expansion interface via a 50 pos IDC connector, J26.
The expansion interface also includes UART (see UART multiplexing), I2C and SPI interfaces. These
additional interfaces are for identifying external displays (via configuration I2C-E2PROM) as well as
touch screen controllers. An external LCD pixel clock can also be supplied via the expansion
connector.
The LCD expansion connector carries 18 data bits per pixel by default (6 per RGB color). The
LPC3250 LCD controller can produce 24 data bits per pixel and it is possible to output all these signals
on the LCD expansion connector. The trade-off is that the UART and I2C serial interfaces have to be
removed. Via SJ6-SJ11 it is possible to select what signals to make available on the LCD expansion
connector. By default pad 1-2 are connected on SJ6-SJ11.
For performance reasons (on the LPC3250), a system with 16-bit color information per pixel is typically
what is implemented. A 565-system is most commonly used. This means 5 bits for red, 6 for green and
5 for blue - 16 bits in total. 24-bit systems will double to load on the external memory bus since each
pixel is stored as 32-bits (instead of 16-bits, or fewer).
Note that the LCD Expansion Connector only supports connecting to a display via the RGB interface.
Some lower resolution displays have the option to connect via a memory bus-like interface, typically 8
or 16-bit. If a memory bus-like interface shall be used, use the external memory bus available via
expansion connector J4 instead.
Also note that JP34 shall have a jumper in position 2-3 when working with the LPC3250.
There are many steps to consider when connecting a custom LCD to the LCD Expansion Connector.
 As a first step, the pixel color signals must be matched between the LPC3250 and display.
The LPC3250 has many options for routing the pixel data to different pins and there are
differences depending on the display mode selected. The OEM Base Board supports the
default settings when using TFT 4:4:4 or TFT 5:6:5-mode. For 24-bit systems, the extra serial
interfaces on the LCD Expansion Connector must be traded-off.
o Many displays have 24 or 18 bit color interfaces, i.e., 8 or 6 bits per color. This
means that some color information is missing when using TFT 4:4:4 or TT5:6:5-
mode. Always connect the available color bits from the LPC3250 to the MSB bits. A
common solution is to connect the most significant color bit to the missing (LSB) bits.
Alternatively, just ground the LSB bits.
o The table below lists where the pixel color information can be found when working in
TFT 4:4:4 or TFT 5:6:6 mode.
LCD-VD bit in
LCD Expansion
Connector, J26
J26 pin
TFT 4:4:4 mode
TFT 5:6:5 mode
LCD_VD4
7
RED0 (LSB)
RED1
LCD_VD5
8
RED1
RED2
LCD_VD6
9
RED2
RED3
LCD_VD7
10
RED3 (MSB)
RED4 (MSB)