Posted on May 17, 2011 at 12:45If you need guidance quickly I present this:
Character modules can operate with just 6 outputs - 4 data, an RS and E strobe. RS=H is data, RS=L is command. We do not recommend this - you will condemn yourself to ''text-only'' modules by electing 4 bit only data. By using 8 bit data and 4 control lines you can extend all the way up to QVGA (320x240) Graphic Lcds.
Major areas requiring attention:
a) Contrast pin (usually pin 3) will normally be adjusted ''near'' 0V (gnd). You should just be able to see the dot field when the display has been cleared. If the voltage is too positive the display will be unviewable.
b) Allow for the set-up time between RS and E. This means that data and RS can be loaded in 1 instruction but E must wait for a 2nd instruction (to set) and a 3rd (to clear). If you employ an 8 bit bus this will extend to 4 instructions: data, RS, E-Hi, E-Lo. *** Should you be using a new FSMC part you can tie to FSMC bus and achieve a display transaction in a ''single'' instruction.
c) When you clear the Lcd (RS=L, data=0x01) the Lcd will ''go busy'' for almost 2mS. You must insert delays or ''read the Lcd's busy flag'' to prevent loss of subsequent data.
d) Basic character writes require ~40uS for the Lcd to execute. Again you need delays/busy read to prevent over-writes.
e) These displays do not nicely shift from line 1 to 2, and from line 2 to 3 or 3 to 4. You have to track the cursor - and implement this cursor write in your software.
f) Remember to initialize the Lcd - vitally important should you elect 4 bit mode. Add extra length delays during this initialization process.
It is often desirable to read stored messages from an 8 pin eeprom and to read ''live'' data coming from a serial port. The Lcd contains 80 bytes of ram (even a 2x16) and you should use this where/when possible. Should more data be arriving you need to dedicate a buffer w/in STM32.
This should get you going - by the way - in ''most'' cases a 5V Lcd will accept the STM32's 3V3 data & control levels - when the Lcd is powered with 5V. Should you power the Lcd with 3V3 it is likely that you will have to adjust the pin 3 ''contrast'' pin below ground. (2-3V negative should do - but this is maker/module dependent)
[ This message was edited by: jj.sprague on 23-09-2008 06:12 ]
