User manual

LPC3250 Developer’s Kit v2 - User’s Guide
Page 63
Copyright 2013 © Embedded Artists AB
Few displays allow for read back of internal control registers via SPI. Only write
transfers are typically supported.
 Many displays have strict requirements of power sequencing during power up and down.
Embedded Artists display boards has an I2C-GPIO expansion chip (PCA9532) and voltage
control of +3.3V and +5V to allow power sequencing.
o Embedded Artists recommend that the power sequences outlined in the display
datasheets are followed for best long term performance of the display.
 For simplicity, Embedded Artists has added a configuration i2c-e2prom in the display add-on
boards that contains information about the connected display. This simplified development of
portable software.
o A standard 24LC64 chip is used with i2c-address 0x56 (1.0.1.0.1.1.0.rw). A0 on the
chip is connected to GND and A1/A2 to VCC to get address 0x56.
 Some displays also require a reset signal after VCC/VDD has stabilized. In that case the I2C-
GPIO expansion chip can be used to create this signal. Alternatively a free GPIO signal in the
LCD Expansion Connector can be used.
 All TFT LCDs must have a control for backlight. A constant current source is needed. Some
displays have one LED string while others have 2-4 strings making control slightly more
complicated.
o OLEDs do not require separate backlight since the pixels transmit light themselves.
 As a final step a touch screen interface is typically needed.
o Embedded Artists display boards often use the TSC2046 from TI. It has a simple SPI
interface.
o Capacitive touch screen controllers typically have I2C or SPI interfaces.
 Do not forget that some displays have configurations pins for selecting interface type
functionality.