Maximun Cable Length for PIC to LCD

**wildbilly** · - 3rd December 2007, 01:23

Hi Darrel. I am using Microcode Studio.

**Darrel Taylor** · - 3rd December 2007, 01:47

Great. That makes it easy.

After installing MPLAB ...

In MCS, go to the View | Compile and Program Options | Assembler Tab

Click the Find Manually ... button and point it to
C:\program files\microchip\mpasm suite

Then check the Use MPASM checkbox.

You should be good to go.
<br>

**Darrel Taylor** · - 3rd December 2007, 01:55

OOPs, one more thing to get that to compile.

In your PBP folder, open the 16F877A.INC file, and comment out the __config line with a semicolon ;

Now you should be good to go.

mister_e,

At least now I know where to go if I need some extra wire.
Sheesh.

<br>

**wildbilly** · - 3rd December 2007, 03:40

Hi Darrel. I have installed MPLAB IDE v8.00 Full Release and setup was done as mentioned.
Now when compiled I get the MPASM window showing the process and then shows 18 errors.
This goes by very fast and starts green and then goes red. The errors are similar to what I had before. Here are a few. I have omitted the path for each error.

205 : Found label after column 1. (WritePort)
205 : Illegal opcode(_Char)
234 : Illegal opcode(_LCD_DATAUS)
249 : Found label after column 1.(DelayUS)
267 : Illegal opcode(LCD_COMMANDUS)

and many more

**Darrel Taylor** · - 3rd December 2007, 04:24

Arrrrgh!

Sorry to put you thru all this, it shouldn't be that hard.

I can't really say what's happening from the errors you showed.
I could probably see what's wrong if you could send the .LST file.

It'll be too big to post, but you could email it to
darrel at pbpgroup.com

It should've worked

<br>

**nomad** · - 3rd December 2007, 14:08

you all must have cringed when i posted my first blinky on bread board. lol mine are true ratsnests. guess it's time to buy some neato jumpers and stop being a disgrace. sniff lol

**mister_e** · - 3rd December 2007, 16:11

Originally Posted by Darrel Taylor

mister_e,

At least now I know where to go if I need some extra wire.
Sheesh.

<br>

Have a look at the last lines of the link... About The Author..

i'm afraid

**mackrackit** · - 3rd December 2007, 16:54

Have a look at the last lines of the link... About The Author.. i'm afraid

And to think I did not have to go to school to be that messy

dideco · - 4th December 2007, 10:10

A CMOS chip as a buffer (such as 4050) can be added to the parallel cable to use longer wires. Also some resistors will help to make a kind of current loop by placing 2.2-4.7 Kohms close to inputs of the LCD unit.

LCD_Lines CON 2 ' # of Lines on LCD, 1 or 2 (Note: use 2 for 4 lines)
LCD_DATAUS CON 50 ' Data delay time in us
LCD_COMMANDUS CON 2000 ' Command delay time in us

"Data delay time" should be longer, such as 500 microseconds or longer. This will help the commads to reach display safely. Pulse decreases because of cable capacitance and resistance (RC time constant). LCD displays can load data in its register buffers in a very short period but cannot execute it as fast as loading. Thats why command delay time is 40 times longer.

**wildbilly** · - 8th December 2007, 20:06

Thanks Dideco for your input, I will carry on with Darrel's method for now as I find it quite interesting and I have been at it for a while. Darrel, here is what I have found so far. I have been able to get your Hijack routines to work without any errors. I am now able to see a perfect display on long lengths of cable. I have tried 20 to 40 ft of 22 awg multi-cable and the display is perfect. I did not need to adjust any delays. I have not been able though, to get the displays to switch properly using the method you described for your 2 LCD's on one pic display method. Have a look at Display_1 and you will see the display is correct using your sample code. On Display_2 you will notice that there are problems on both displays when using the hijack routines.

Thanks.