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new and confused


New member
I am new to the whole LCD's. In fact I purchased the Crystal Fontz 636 serial three weeks ago while I was in the process of moding my case. I finished the case two days ago and tried to instal the lcd. I am not sure what I am doing wrong but I can not seem to get it to work. I am running the lcd on xp professional and have only installed lcddriver software and motherboard monitor 5.0 No other lcd software is installed. When I try to access the lcd driver software I get a prompt saying that the lcd is in use by another aplication or locked. I am not exactly certain what that means but I checked my jumpers on the lcd and all of them are open. When I checked my device manager I have not noticed any other new devices under the com settings. Should it be showing up. When I do a search the lcd will light for a second and then go off. I guess I am just curious if I have not installed the software correctly or if i am just missing a needed aplication. One other thing. I have noticed that my modem does not respond when I plug in the lcd. Even if I change it to another com setting. Any help would be greatly appreciated. Thank you and I hope everyone had a good Easter.
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CF Tech

The "636" is a "HD44780" compatible LCD. These are also commonly referred to as "parallel" or "character" LCDs. I believe that LCDriver only supports the "serial" interface modules.

The 636 page has the 636 data sheet, although if you purchased it recently, it is probably the replacement CFAH1602B module.

First, please read the disclaimer here:


The schematic used is determined by the software, not the display. The most common schematic is shown below. Please determine which software you are going to use, then see what schematic it recommends.

If you decide to use this schematic, then use CFAH_WinTest to make sure your wiring job works. Once that is all going, CrystalControl will work with the LCD.

Here is a page about 44780 based LCD's in general.

Here is a tutorial on a typical LCD parallel connection to a PC's printer port:


Then click on "LCD Display", and then "Step by Step how to build an LCD Display" (it is a framed site).

Another "Hooking up parallel LCDs" Article:


Both of these use this common schematic, less Rlimit:

We do not recommend using a potentiometer alone for the backlight. It is too easy to ruin the backlight by turning the pot too far. You should calculate the limiting resistor as described in this post to limit the maximum current (and set the maximum brightness) and then put that in series with a pot if you want to dim the backlight.

Here are some pages with some general LCD connection details:


New member

I apologize but I typed the wrong display model in. I have the 634 serial and not the 636. I am going to remove my modem and attemp it without it in place to see if I am getting a conflict. Thank you for taking the time to read and post a reply.

CF Tech

I was wondering where you had found a 636 :)

Try to get it going with WinTest, that will assure the hardware and connections are correct.


New member
got it figured out

I got it going last night. My modem and a lcd were conflicting. I moved the modem to my last PCI slot and I had a crystal fontz lcd lit up and waiting to go. It was wierd how Device Manager couldn't find a problem with the port. It is usually good at pointing those problems out. Thanks for the help.