<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"> <HTML ><HEAD ><TITLE >Parallel Port Troubleshooting</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.7"><LINK REL="HOME" TITLE="LCDproc User's Guide" HREF="book1.html"><LINK REL="UP" TITLE="LCDproc Drivers" HREF="c429.html"><LINK REL="PREVIOUS" TITLE="LCDproc Drivers" HREF="c429.html"><LINK REL="NEXT" TITLE="The Matrix Orbital Driver (MtxOrb)" HREF="x846.html"></HEAD ><BODY CLASS="SECT1" BGCOLOR="#FFFFFF" TEXT="#000000" LINK="#0000FF" VLINK="#840084" ALINK="#0000FF" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="3" ALIGN="center" >LCDproc User's Guide: The Ultimate Guide to LCDproc 0.4.3</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="bottom" ><A HREF="c429.html" ACCESSKEY="P" ><<< Previous</A ></TD ><TD WIDTH="80%" ALIGN="center" VALIGN="bottom" >LCDproc Drivers</TD ><TD WIDTH="10%" ALIGN="right" VALIGN="bottom" ><A HREF="x846.html" ACCESSKEY="N" >Next >>></A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="PPTTROUBLE" ></A >Parallel Port Troubleshooting</H1 ><P >Unfortunately attaching an LCD module to a parallel port is not trivial.</P ><P >In most cases it requires soldering abilities and basic knowledge of electronics.</P ><P >The following hints might be helpful:</P ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="PPT-CHECK-WIRING" ></A >Check The Wiring</H2 ><P >Wiring errors can easily be made. If you are unexperienced with the soldering iron better have someone solder it for you. Display modules are sensitive to electro static discharges, so touch an earthed surface (computer case, water pipes...) before you handle these.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="PPT-POWER" ></A >Power Source Unregulated / Noisy</H2 ><P >Make sure your power supply delivers steady 5 Volts with- out noise or interruptions. The bare wall plug in trans- former is not suitable, though you can make it stabilized by adding an 7805 and a few capacitors. Some noise induced in the supply lines my be tricky to track, even if you have an oscilloscope.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="PPT-GND-LIFT" ></A >Ground Lift</H2 ><P >The power supply wires and especially the GND wires should be a little thicker than the other wires. If GND is not thick enough (or not existent, see 1) the resistance of the wire may cause differing GND potentials in the circuit. This may lead to strange display behaviour. It may also be wise to solder a 100nF capacitor directly to the GND and VDD pins of the display.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="PPT-LATCHUP" ></A >Latchup</H2 ><P >Never let the supply voltage get much below the io signal voltage. It may lead to a latchup condition which will destroy the controller chip on the display.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="PPT-CONTRAST" ></A >Contrast</H2 ><P >If you don't see anything on your display it may be that your contrast voltage is set wrong. Turn your contrast potentiometer all the way to the end connected to GND. Contrast is highest then.</P ><DIV CLASS="NOTE" ><P ></P ><TABLE CLASS="NOTE" WIDTH="100%" BORDER="0" ><TR ><TD WIDTH="25" ALIGN="CENTER" VALIGN="TOP" ><IMG SRC="./stylesheet-images/note.gif" HSPACE="5" ALT="Note"></TD ><TH ALIGN="LEFT" VALIGN="CENTER" ><B >Beware</B ></TH ></TR ><TR ><TD > </TD ><TD ALIGN="LEFT" VALIGN="TOP" ><P >The module you got so ultra cheap may be an enhanced temperature model which needs a negative contrast voltage for sufficient contrast - see chapter 99 on how to make negative voltage.</P ></TD ></TR ></TABLE ></DIV ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="PPT-VOLTAGE" ></A >Parallel Port Voltage</H2 ><P >Many modern mainboards and especially notebooks will not nearly output 5V for a logic H as the older parallel ports did, because the operating voltage of computers is lower than 5V these days. I have measured voltages between 2.5V and 4V for logic H, which is barely within specification of the HD44780. If you account RCL of your cable, this may not be enough and can cause unreliable operation.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="PPT-SIGNAL-RISE-TIMING" ></A >Enable Signal Rise Time</H2 ><P >If you ever read the HD44780 datasheet you will notice that somewhere in the 'signal timing' table is written: 'Enable Signal Rise Time max. 20nS'. That means the Voltage on the HD44780 pin called 'Enable' has to rise from 0 Volts to 5 Volts within 20 Nanoseconds and the other way round. They should better print that in big fat red letters, because most HD44780s are really picky about the enable signal rise time.</P ><P >That is a Problem: If you count together the bad driving characteristics of the parallel port combined with the capacitance of flat ribbon cable you may easily get an order of magnitude slower rise time. Therefore you should only use really short cable ( shorter than 50cm) for connecting the display to the parallel port. It may also be useful to use pull-up resistors on the display module or a schmitt-trigger.</P ><DIV CLASS="NOTE" ><P ></P ><TABLE CLASS="NOTE" WIDTH="100%" BORDER="0" ><TR ><TD WIDTH="25" ALIGN="CENTER" VALIGN="TOP" ><IMG SRC="./stylesheet-images/note.gif" HSPACE="5" ALT="Note"></TD ><TD ALIGN="LEFT" VALIGN="TOP" ><P >The rise time of a digital output can (usually) not be altered by Software.</P ></TD ></TR ></TABLE ></DIV ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="PPT-EMI" ></A >EMI</H2 ><P >The cable from the parallel port to the display may be sensible to electromagnetic interference and may emit electromagnetic radiation. If you place your cellphone near the cable, you may get unexpected display readings, on the other hand your house neighbour may not be able to listen to his/her favourite radio station any more - so better use shielded cable and put the display in a metallic case, perhaps a computer case.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="PPT-BLACK-LINES" ></A >One or Two Black Lines</H2 ><P >If you see one or two black lines on the display it means nothing more than that the display is powered and contrast voltage is present. If one or two black lines appear the controller has not been reset properly by the on chip power on reset generator. No need to worry - it will be reset by the <TT CLASS="APPLICATION" >LCDd</TT > software. But if the black line will not disappear although the wiring is working, the controller on the display may be defective.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="PPT-TOO-FAST" ></A >Software Too Fast</H2 ><P >If you have a super GHz computer it may happen that the signal timing generated by <TT CLASS="APPLICATION" >LCDd</TT > is too fast. Adjust DELAYMULT in the source file to a bigger value. Parallel port wirings usually don't permit to read back the busy flag of the controller chip, so timing must be adjust so that the controller never is busy.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="PPT-BACKLIGHT" ></A >LED Backlight</H2 ><P >Check whether you need a resistor for your LED Backlight and which value it should have. If you forget the required resistor the backlighting LEDs might become hot and draw excessive current.</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="PPT-HD44780-COMPATIBLE" ></A >HD44780 Compatible</H2 ><P >The original HD44780 controller that we advertise to support has become the industry standard for alphanumeric character displays. The original HD44780 is out of production. It has many successors from many manufactures, which sometimes won't tell you that their chips are 'compatible'.</P ><P >To name a few: KS 0066, KS 0070, KS 0076, LC 7985, NT 3881, SED 1278, ST 7066 ...</P ></DIV ><DIV CLASS="SECT2" ><H2 CLASS="SECT2" ><A NAME="PPT-MISC" ></A >Miscellania</H2 ><P >This text has originally been taken from a <A HREF="http://lists.omnipotent.net/pipermail/lcdproc/2002-May/005832.html" TARGET="_top" >message</A > by Robin Adams <TT CLASS="EMAIL" ><<A HREF="mailto:robin@adams-online.de" >robin@adams-online.de</A >></TT ></P ><P >Converted to docbook and slightly modified May 2002, Rene Wagner <TT CLASS="EMAIL" ><<A HREF="mailto:reenoo@gmx.de" >reenoo@gmx.de</A >></TT ></P ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="c429.html" ACCESSKEY="P" ><<< Previous</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="book1.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="x846.html" ACCESSKEY="N" >Next >>></A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >LCDproc Drivers</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="c429.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >The Matrix Orbital Driver (MtxOrb)</TD ></TR ></TABLE ></DIV ></BODY ></HTML >
