Maximun Cable Length for PIC to LCD

**Darrel Taylor** · - 28th December 2007, 20:16

That's Great wildbilly.
And Happy New Year to you too.

I was hoping it would go the 40ft. but wasn't sure.

Don't want to ruin it for you if you're still trying to do 3 LCD's, but I can show you how, if you give up.

regards,

**wildbilly** · - 29th December 2007, 20:00

Hi Darrel. I would like to know how to do 3 LCD's. I won't turn down a chance of learning more. Thanks

**Darrel Taylor** · - 31st December 2007, 08:23

OK, let's go with the learning ... idea ...

Here's the changes to add 1 more display to what we already have.
Mostly, it's just "more of the same".

These are the same 3 sections that were modified the last time.
New changes are in red ...

Main Program

Code:

;----[ Change these to match your LCD ]---------------------------------------
LCD_DB4   VAR PORTB.0
LCD_DB5   VAR PORTB.1
LCD_DB6   VAR PORTB.2
LCD_DB7   VAR PORTB.3
LCD_RS    VAR PORTB.4

LCD_E1    VAR PORTB.5
LCD_E2    VAR PORTB.6
LCD_E3    VAR PORTD.0   

LCDEN     VAR BYTE BANK0  ; Enable bits for each LCD
  LCD1EN  VAR LCDEN.0
  LCD2EN  VAR LCDEN.1
  LCD3EN  VAR LCDEN.2

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 

INCLUDE "LCD_AnyPin.pbp"  ; *** Include MUST be AFTER LCD Pin assignments ****
LOW LCD_E1              ; Start with Enables OUTPUT LOW
LOW LCD_E2
LOW LCD_E3

LCD_AnyPin.pbp

Code:

ASM
LCD_Port_HNIB  macro           ; Port definition for LCD High Nibble
    Vbit   LCDCDFLAG, _LCD_RS  ; Select Command/Data register
    DelayUS  2
    NOP
    Vpin   4, _LCD_DB4         ; Put the High Nibble on the bus
    Vpin   5, _LCD_DB5
    Vpin   6, _LCD_DB6
    Vpin   7, _LCD_DB7
    DelayUS  2

    btfsc    _LCD1EN           ; Set enable(s) High
    bsf      _LCD_E1
    btfsc    _LCD2EN
    bsf      _LCD_E2
    btfsc    _LCD3EN
    bsf      _LCD_E3
    DelayUS  5                 ; hold for 5us
    bcf      _LCD_E1           ; Enable(s) Low - Clocks data
    bcf      _LCD_E2
    bcf      _LCD_E3
  endm
;-----------------------    
LCD_Port_LNIB  macro           ; Port definition for LCD Low Nibble 
    Vpin   0, _LCD_DB4         ; Put the Low Nibble on the bus
    Vpin   1, _LCD_DB5
    Vpin   2, _LCD_DB6
    Vpin   3, _LCD_DB7
    DelayUS  2

    btfsc    _LCD1EN           ; Set enable(s) High
    bsf      _LCD_E1
    btfsc    _LCD2EN
    bsf      _LCD_E2
    btfsc    _LCD3EN
    bsf      _LCD_E3
    DelayUS  5                 ; hold for 5us
    bcf      _LCD_E1           ; Enable(s) Low - Clocks data
    bcf      _LCD_E2
    bcf      _LCD_E3
  endm
ENDASM

LCD_AnyPin.pbp

Code:

;----[Initialize the LCD]-------------------(DO NOT Change)-------------------
LCD_Init:
@   OutputPort  LCD_Port_HNIB    ; Set LCD bus to OUTPUT
    LCDEN = %111                 ; Initialize all LCD's at the same time
    LOW LCD_RS                   ; Start with RS LOW
    Char = 3   : gosub  LCDsendShortCOM : @  DelayUS 6000
                 gosub  LCDsendShortCOM : @  DelayUS 1000
                 gosub  LCDsendShortCOM : @  DelayUS 1000
    Char = 2   : gosub  LCDsendShortCOM : @  DelayUS 1000  ; Start 4-bit mode
    Char = $28 : gosub  LCDsendCOM  ; Function Set, 4-bit, 2-line, 5x7
    Char = $0C : gosub  LCDsendCOM  ; Display ON
    Char = $01 : gosub  LCDsendCOM  ; Clear Screen
    Char = $06 : gosub  LCDsendCOM  ; Entry Mode
    LCD_Initialized = 1             ; LCD has been Initialized
goto LCDAfterInit

And then, to use it.
It still works the same as before.
But now it's easier to treat the Enable bits like a binary number.
With each bit representing a different display ...

Code:

    LCDEN = %001
    LCDOUT $FE,$80, "Display 1"
    
    LCDEN = %010
    LCDOUT $FE,$80, "Display 2"

    LCDEN = %100
    LCDOUT $FE,$80, "Display 3"
    
    LCDEN = %111
    LCDOUT $FE,$C0, "ALL Displays"

And that should be it.<hr>
Now, Even though this all works fine ...
I don't like it.

After making all the changes to get 3 LCD's to work.
It's still limited to 3 LCD's.
If you want 4, then you have to go modify it again.
Then if you want to use 2 LCD's on another project. It'll throw a bunch of errors, that won't make sense 6 months from now.

Then there's the Timing options.
What if the cable is longer? Or shorter? How do you adjust the delays?

So what I've done, is create a new module that should incorporate everything learned here, and allow everyone to have up to 8 LCD's on long or short cables without to much hassle.

But it takes longer to post the thread, than it does to write the program.

And I Gotta work tomorrow too.

Feel free to use the code I just posted (it should work)
Or you may want to wait for my next post in the PBP Extensions forum. (day or two)<hr>
P.S. It's unfortunate that we still won't know the answer to your first question.

Originally Posted by wildbilly

What is the maximum cable length of cable that can be used between Pic and LCD?

Uhhh, 40 ft, as far as we can say.
But who knows?
<br>

skimask · - 31st December 2007, 09:25

Question from the sidelines...maybe an idea...not sure...haven't looked into it yet...

Couldn't the LCDOUT command itself be 'hi-jacked' inside on of the macros to change the E line assignment dynamically? As far as I know, LCDs won't do squat unless the E line is pulsed.
Maybe something like:
LCDOUT $fe , $fe , 0 , "First LCD"
LCDOUT $fe , $fe , 1 , "Second LCD"
LCDOUT $fe , $fe , 2 , "Third LCD"
....and so on and so on...
As far as I know, there aren't any character LCDs any wider than 40 characters. If the second character in the 'string' was anything above $FC, it could be a 'hijack' command...
or something like that anyways...
As for myself, like I said before, I'm running 3 different types of LCDs on my OBD interface right now (16x2 parallel, 122x32 graphic mode, and a 130x130 Nokia color knockoff).
Guess which one is the easiest to interface with?

**Darrel Taylor** · - 31st December 2007, 11:07

Originally Posted by skimask

Maybe something like:
LCDOUT $fe , $fe , 0 , "First LCD"
LCDOUT $fe , $fe , 1 , "Second LCD"
...

Sure,

With complete control of the LCDOUT command, you can do pretty much whatever you want.

And, It's not a bad idea.

So, with the existing code from this thread.
Changing the LCDsend routine like this ...

Code:

;----[Send a byte to the Virtual LCD PORT]------------(DO NOT Change)---------
TempChar        var  byte
Char            VAR  Byte
LCD_Initialized VAR  FLAGS.1
RSS             VAR  FLAGS.0                ; LCD RS State
HJ_Command      VAR  BIT

;----[ This routine is called once for every character sent by LCDOUT ]-------
LCDsend:
      @  MOVE?AB  _TempChar                 ; Get char sent by LCDOUT, in WREG
      if !LCD_Initialized then LCD_Init     ; Make sure LCD was Initialized 
  LCDAfterInit:

      IF HJ_Command then LCDEN = TempChar : HJ_Command = 0 : goto LCDsendDone
      IF RSS then NO_HJcheck
      IF TempChar = $FE then RSS = 1 : HJ_Command = 1 : goto LCDsendDone
  NO_HJcheck:

      if TempChar = $FE then RSS=0 : goto LCDsendDone ; next char is Command 
      Char = TempChar
  LCDsendCOM:
      @  WritePort   _Char, LCD_Port_HNIB   ; send the High Nibble
  LCDsendShortCOM:
      @  WritePort   _Char, LCD_Port_LNIB   ; send the Low Nibble

      IF RSS = 0 then                    ; Is a Command
          IF Char = 1 then CommandDelay     ; Long delay for Clear Screen
          IF Char = 2 then CommandDelay     ; Long delay for Home
          @  DelayUS   _LCD_DATAUS          ; Short delay for everything else
          goto DelayDone
      else                                  
          @  DelayUS   _LCD_DATAUS          ; Short delay for Data
          goto DelayDone
      endif
  CommandDelay:
      @  DelayUS   _LCD_COMMANDUS
  DelayDone:
    if LCD_Initialized then RSS = 1       ; Set RS to Data next time
  LCDsendDone:
return

Then you can embed the LCD selection inside the LCDOUT statements...

Code:

    LCDOUT $FE,$FE,%001, $FE,$80, "Display 1"
    LCDOUT $FE,$FE,%010, $FE,$80, "Display 2"
    LCDOUT $FE,$FE,%100, $FE,$80, "Display 3"
    LCDOUT $FE,$FE,%111, $FE,$C0, "ALL Displays"

And it still works the original way too. (Choices)

Code:

    LCDEN = %001
    LCDOUT $FE,$80, "Display 1"
    
    LCDEN = %010
    LCDOUT $FE,$80, "Display 2"

    LCDEN = %100
    LCDOUT $FE,$80, "Display 3"
    
    LCDEN = %111
    LCDOUT $FE,$C0, "ALL Displays"

Now I really gotta go to bed.

skimask · - 31st December 2007, 23:03

Originally Posted by Darrel Taylor

And, It's not a bad idea.

I get 'em once in a great while...

So, with the existing code from this thread.................

and here I spent the better part of a few hours last night messing with the core macros.
I'm digging this idea much better. (Yes, I said 'digging'

)

**Darrel Taylor** · - 31st December 2007, 23:33

Maybe you'll Dig this idea too.

GLCD's using LCDOUT.

<br>

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