readme

最新的LPC214X LCD驱动程序

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--  $Id: README 279 2008-11-03 23:51:30Z jcw $
--  $Revision: 279 $
--  $Author: jcw $
--  $Date: 2008-11-03 18:51:30 -0500 (Mon, 03 Nov 2008) $
--  $HeadURL: http://tinymicros.com/svn_public/arm/lpc2148_demo/trunk/lcd/README $
--

This code should drive any HD44780 based LCD controller, but it's been tested
with CrystalFontz CFAH1602Z-YYH-ET display.  There is an application note that
recommends this display family for 3.3V operation.     This display does have
one rather bothersome quirk: the backlight needs 4.1 volts.  3.3V is not enough
to drive it to adequate brightess, and 5V will fry it.  In a design that made
use of this display, a Sharp PQ1R40 regulator was used.  The LCD product page
is at http://www.crystalfontz.com/products/product.phtml?product_id=524 

lcd_4bit.c is for interfacing to LCDs with a 4-bit interface.  There's not
enough I/O on the Olimex LPC-P2148 to drive the LCD in 8-bit mode, so this is
the example to use.

lcd_8bit.c is for interesting to LCDs with an 8-bit interface.  This basic code
works on another platform, but it's untested as distributed.  It *should* work,
however.  And if there are any problems, they should be very minor, and
probably revolve around actual port I/O.

CrystalFontz has a nifty little negative bias charge pump circuit that uses two
diodes, two capacitors and a resistor.  Using the one of the PWM channels, you
can vary the contrast in software by changing the duty cycle of the PWM.  The
demo code already has support to demonstrate the PWM usage (although it
requires an oscilloscope to see).  

The docs/biaspump.png file shows the backlight regulator circuit and the
negative bias charge pump circuit.  For the Olimex LPC-P2148 board, connect
P0.21 to LCD_Vo.  I find that about -1.5V gives a nice contrast ratio.