8051-to-LCD Interface
Yet Another 8051-to-LCD Interface
The Web is littered with examples of how to control the standard
Hitachi-44780 LCD using an 8051 micro. So, you may ask, “Why
bother doing another?”
A bunch of reasons:
I hate everybody else's code. Call
it “NIH.” I don't care. There. I've said it. (You'll
probably hate my code, too. I understand and accept your
judgment.)
Most of the examples I've seen are
written in assembly, and quite frankly, I would rather not deal with
assembly language if at all possible.
Some of the examples used the
nybble interface to the LCD; I wanted to use the byte-wide
interface.
Some examples had various latches or other logic between the
micro and the LCD; I wanted a glueless interface (at the cost of
extra micro port I/O pins).
So, here is my LCD interface code. I compiled this using the Keil
C51 compiler, v7.04. My target is the Silicon
Labs (Cygnal) C8051F231
micro, but I suppose any 8051 variant with enough free port pins (all
eight bits of Port 1 for the data I/O bus plus three control signals)
will work. No glue logic between the micro and the LCD is required. I
like the Cygnal parts because they have built-in flash and in-circuit
emulator support via JTAG, and the RS-232-to-JTAG
emulator dongle costs only $65! (Buy the prototyping
board for only $99!) I mean, that's a screeeeeeaming deal,
especially if you remember having to pay five large for the old
ISA-bus Nohau emulator with the bond-out chip. (And you probably also
remember blowing up the bondout chip just as a deadline was
approaching!)
I used an Optrex DMC-16202NY-LY-AGE
(pdf) 16-character by 2-line LCD module, mainly because DigiKey had
them in stock and they weren't all that expensive.
The only bit in the code that is Cygnal-specific is in the private
isLcdBusy() function in lcd.c. The register
PRT1CF is manipulated to allow port 1 to be read as an
input.
Sources
lcd.h:
header file that holds the function prototypes.
lcd.c: C
source for LCD interface functions.
lcdcmd.h:
header file that holds some convenient constant definitions (used by
lcd.c and not needed by "the outside world")
To use, simply add lcd.c to your Keil project, add
lcd.h to whatever sources may call the functions in
lcd.c and off you go. Be sure to call the LcdInit()
function before calling anything else.
Pin Assignments
My code specifies the following micro
port pin-to-LCD-signal assignments:
Oh, yeah, don't forget to wire the micro to the LCD pins, and make
sure the LCD bias is set to something that will actually display the
characters. Powering the LCD helps, too.
Technical Support
I can probably help you get this code working on your particular
8051 flavor. Send me a note at devel@latke.net. I've built things
using the original Intel
87C51, the Dallas Semiconductor (now Maxim) DS5000T,
the TI TUSB3200A
and the aforementioned Cygnal chip. Sorry, can't help you with Moto
HC05/08/11 or PIC or any other microcontroller family, but hey, a
micro is a micro, so porting the code oughta be fairly obvious.
Some real good LCD interfacing info is available at Myke Predko's
LCD Interfacing Reference Page.
The good folks at 8052.com
have a really good tutorial
you might like to read.
Also, see Peer's
LCD Pages.
I've played with the Small
Device C Compiler (sdcc) but its syntax is not (or at least
wasn't, last time I looked) compatible with Keil. Good luck if you
choose to use it.
I cannot help you do your homework assignment, so please don't
ask. Pester the people at news:comp.arch.embedded
instead.
Disclaimer and copyright.
This code is ©
2004 by Andy Peters, ASP Digital. All rights reserved. I suppose that
this code is now officially Open Source, and while I am not
up-to-date on the differences between the GPL, the LGPL, the BSD and
other open-source licenses, I'm sure that at least one of them
applies. You may use this code as you see fit. If you use it, please
drop me a note at devel@latke.net and tell me! If you publish it,
make sure to include my copyright information.
I make no guarantees or warranties whatsoever about this code. (In
other words, if you use it as part of a flight-control system and the
plane crashes, it is not my fault. You should have done your due
diligence and some proper testing.) I also do not warrant that this
code is free of anyone's intellectual property claims.
