Talkback for article: 258, September2002

Understanding HD44780 compatible LCD-displays

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From: Mariusz Kozlowski <sp3fxc(at)> [ date: 2002-10-31 ]
I've connected LCD (20x2) with HD66702 chip to my computer. It works ok, but I had to rewrite some parts of code in order to corectness of displayed data.The problem was that in the second line not all chars were displayed.To solve this problem I've changed the lenght of strings to be displayed in second line. Maybe it's not best solution but after all it works :)
Have fun!
From: Michele [ date: 2002-12-03 ]
I have connected LCD (40x2) with PIC 16F84A. When i try to display a word with more than 8 byte onl the first 8 byte are dislayed either in first lines or in second lines.
Can anybody help me?
From: Szymon Smakolski <ninevolt(at)> [ date: 2003-02-02 ]
Great article. Just one thing..
Google around and you can oodles of pages dedicated to wiring an LCD to your parallel port. Although this may have practical applications in some situations (?), I find it to be a lot more interesting to be able to interface the *device* with the LCD readout to your PC. i.e. I want my C program to be able to access temperature data via the parallel port (as opposed to sending data to an LCD via the parallel port :P). I have a ~$10 Springfield (R) PreciseTemp (TM) digital thermometer. It has dual zone sensors (one in the thing and one at the end of a 6' wire). The LCD panel is 2 lines of 4 digits each (with a decimal and a few little other things around). I took it apart and realized that there's about 30 (tiny) pins for this sucker.. In any case, after I somehow figure out a way to patch some of the outputs (30 pins in 3.7 cm. The gaps between them are about .6mm. Any ideas would be appreciated) from the thermometer circuit over to a chopped printer cable, I'll whip up a C program to listen for anything.. Pretty sure I'd be able to figure out the rest from there (assuming I could find the 'Enable' bit)

Anyways, my point is that I've never seen something like this covered, and you seem like you know what you're doing :P Help me out, I'm a first year EE student and I have no idea what I'm doing.
From: Hertz <hertz920(at)> [ date: 2003-05-06 ]
I've connected LCD(20*4)with mcs-51.It works very well.
what about TM12864ABA? Anybody knows ? with Assemble program to match it.
From: Thomas Moller <tkmax1234(at)> [ date: 2003-07-06 ]
Does anybody have the datasheet for HD66702 or just the pin-out configuration. It seems to be impossible to find anywhere...

From: Mathias <mathias.juenger(at)> [ date: 2003-10-20 ]
Hi Jan,

kennst du Bezugsquellen fr das HD44780 (oder Kompatible)?

Bitte auch direkt an die Email-Adresse antworten. Vielen Dank
From: drhawk <drhawk1(at)> [ date: 2004-04-06 ]
i'm a n00b and nothing worxx....
i got some warnings fuction returns adress of local variable with uptime.c cpu.c swap.c etc
whats wrong
and how to start the program when its compiled?
wie starte ich das programm wenns sich doch compile lsst?
From: Daniel <Daniel.Greiser(at)> [ date: 2004-10-07 ]
Hallo Jan,
very exciting page. I have a 2 line Display and would like to switch in 2 line mode. But my display is connected with only DB4 to DB7 in 4 Bit mode. How can I switch in 2line mode? To write a text in the second line, what have I to do?
With best regards
Please answer directly to my Email adress
From: Richard Urwin <richard(at)> [ date: 2005-11-11 ]
Nice page. Thanks for the details of LCD contrast/power, that was the last piece I needed to get the project working.

For what it's worth, changing from 8bit to 4bit is done with three E pulses, the first sets 4 bit mode, the second sets the high bits and the third the low bits. Use DB4-DB7 as the data lines. After the first write to set 4 bit mode, subsequent writes use two E pulses per write; the first sets the high bits, the second sets the low bits.
From: Tomasz Nowak <nowak2000(at)> [ date: 2006-05-05 ]
Po 0x379 jest 0x37A, autor mgłby to poprawić :)
From: YORJANE <yorjaneyaosmel(at)> [ date: 2006-09-07 ]
From: Andreas Jahnke <a-jahke(at)> [ date: 2006-10-14 ]
I used the display on a Linux 2.6 System. Further I modified the sourcecode to get rid of the compile warnings etc. I can download the software under
From: Andreas Jahnke <a-jahnke(at)> [ date: 2006-10-14 ]
I' m using the display on a Linux 2.6 system. Further I modified the source code to get rid of the compiler warnings etc. You can download the software under

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