Hitachi 44780 LCD Controller Display IO

I don't think Peer's site can be improved upon...
http://home.iae.nl/users/pouweha/lcd/lcd.shtml Peer's LCD Pages - How to control a HD44780-based Character-LCD General info and code-examples

Hooking up a small Hitachi 44780 driver type LCD to your PC via the Parallel Port

PIC Specific LCD routines

Atmel AVR, LCD Display driver, PHICO Panel, HD44780, Ray Pasco

Peter [farmerpentium at CWCOM.NET] says:

Developing an LCD driver interface for the LM032LN display took me a lot longer than expected, especially UDGs, and I traced it to quirks in the HD44780A00.

Commands need to be sent twice for reliability. Characters output are no problem though.

The address position command for uploading UDG information needs not only repeating, but also given a settling time - I gave an arbitrary 1.5 ms after each command before sending data.

I also found that "ASCII" 00h, a UDG, is what the display writes as spaces, thus for a clean display this needs to be filled with blanks. Thus I've effectively got only 7 available UDG characters, not 8.

I also found that placing a bit of ferrite around the EN, RS and RW lines seems to help reliability - the circuit is on a breadboard at the moment.

Since the chip will not initialize using busy-polled command routines, I have to use a paced one for initializing, and for simplicity all commands sent are paced. So I'm using a paced driver for sending commands, and a busy-polled driver for sending character and UDG data.

The display is now working reliably, but its had a lot of aggro (over 80 chip rewrites in the course of debugging). So now instead of write piecemeal to the display I've employed the KISS principle, using RAM in the PIC 16F877 as a display buffer - use that and forget display idiosyncrasies... Periodically uploading that to the display takes just over 4 ms. All my PIC routines are interruptible, and the code is written for the PIC16F877.

I've got the EPE Feb-Mar 1997 articles "How to use intelligent LCDs" (and the original magazines), from the vendor of my displays have a photocopied datasheet for the LM032LN, from the internet have 2 or 3 datasheets for the HD44780, have AN587 and from various PIClist-derived websites have various peoples' comments on how-to with this display. It seems they are necessary, sadly. But all the way along, and especially on this list there have been complaints about difficulties with UDGs.

See also:

• /techref/io/lcd/panel1.htm LCD Front Panel Set: 2x16 LCD w/HD44780 controller, 4 push buttons, 3 LEDs and a 2x12 pin header.+
• http://home.iae.nl/users/pouweha/lcd/lcd.shtml Peer's LCD Pages - How to control a HD44780-based Character-LCD General info and code-examples
• http://www.promixis.com/forums/archive/index.php/t-1785.html
  http://w1.864.telia.com/~u86435834/2wire4015_lcd_R2.jpg An HC4015 dual 4 bit shift register takes only two io pins, but allows for E to be generated separately (and time shifted by a clever diode "and" gate with the clock) and for the register to be reset by the MSB when the clocking over flows.
  

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