Custom character problem

[Jack Hoffnung]

I have built a 2-line interface for a 2 x 16 LCD display (based on the old 74LS174), and it works fine, except for custom characters. I wrote the following simple program to create and then display a custom character, based on a program in the help file, but all I get is a blank screen. I have been able to verify that the array elements exist, but do not know why they are either not being copied to the LCD controller, or just not displayed. I am using what I believe is the most recent lcd.h file, dated 8-17-2014. Any help would be appreciated.

    ;Create and display a custom character

    #chip 12F683,8             ;PIC12F683 running at 8 MHz
    #config mclr=on            ;reset handled manually
    #config osc=int             ;use internal clock

    #define LCD_IO 2
    #define LCD_DB    GPIO.0   ;shift register data on GP0, pin 7
    #define LCD_CB    GPIO.1   ;shift register clock on GP1, pin 6

    Dim TempArray(8)

    'Set the array to hold the character

    TempArray(1) = 0b00011011
    TempArray(2) = 0b00011011
    TempArray(3) = 0b00000000
    TempArray(4) = 0b00000100
    TempArray(5) = 0b00000000
    TempArray(6) = 0b00010001
    TempArray(7) = 0b00010001
    TempArray(8) = 0b00001110

    'Copy the character from the array to the LCD
    LCDCreateChar 0, TempArray()

    'Draw the custom character
    LCDWriteChar 0

[Anobium]

@Jack.

This solution is 'based on the old 74LS174' approach. What is the configuration so I can build something similar?

:-)

[Anobium]

@Jack. A simple question. Can you confirm normal string handling works? I built a 74LS174 LCD solution last week and all was OK, but, I did not try LCDCreateChar. Please confirm normal operations is ok.

[Jack Hoffnung]

  Hi Anobium.  Thanks for the reply.  I added a bit to the code to show string
  handling works, and that I can print elements of the array.  I note however that the
  same code placed after the LCDCreateChar command yields nothing.  In fact, the
  screen won’t even clear after that command.  Is this a clue?

;Create and display a custom character

#chip 12F683,8             ;PIC12F683 running at 8 MHz
#config mclr=on            ;reset handled manually
#config osc=int            ;use internal clock

#define LCD_IO 2
#define LCD_DB    GPIO.0   ;shift register data on GP0, pin 7
#define LCD_CB    GPIO.1   ;shift register clock on GP1, pin 6

Dim TempArray(8)
Dim cnt as byte
'Set the array to hold the character

TempArray(1) = 0b00011011
TempArray(2) = 0b00011011
TempArray(3) = 0b00000000
TempArray(4) = 0b00000100
TempArray(5) = 0b00000000
TempArray(6) = 0b00010001
TempArray(7) = 0b00010001
TempArray(8) = 0b00001110

CLS
Print "A string works"     ;This is seen on the LCD
Locate 1,0
wait 2 s
     For cnt = 1 to 8
     Print TempArray(cnt)  ;so are these
     Next
wait 2 s

'Copy the character from the array to the LCD
LCDCreateChar 0, TempArray()

CLS
Print "This one won't"      ;This doesn't show
Locate 1,0
wait 2 s
     For cnt = 1 to 8
     Print TempArray(cnt)   ;Nor do these
     Next
wait 2 s
CLS

'Draw the custom character
LCDWriteChar 0              ;Nor does this

[Anobium]

I have tested on a LCD_IO 4 and all is good.

Please try this. Let me know the results. Add this to your program. It will redirect the method while we determine the root cause.

~~~~

define LCDCreateChar myLCDCreateChar

'Create a custom character in CGRAM
sub myLCDCreateChar (In LCDCharLoc, LCDCharData())

      'Store old location
      #IFDEF LCD_IO 4,8
                Set LCD_RS Off
                LCDLoc = LCDReadByte
                Set LCDLoc.7 On
      #ENDIF

      'Select location
      Set LCD_RS Off
      LCDWriteByte (64 + LCDCharLoc * 8)
      wait 5 10us

      'Write char
      Set LCD_RS On
      For LCDTemp = 1 to 8
                LCDWriteByte LCDCharData(LCDTemp)
                wait 5 10us
      Next

      'Restore location
      #IFDEF LCD_IO 4,8
                Set LCD_RS Off
                LCDWriteByte (LCDLoc)
                wait 5 10us
      #ENDIF

end sub

[Jack Hoffnung]

Hi Anobium,.

    I inserted your code into my program, and got the same results; nothing works
    after the LCDCreateChar command is reached.  The hardware was built exactly as
    shown in the article: Build your own "2-Wire LCD Interface" using the PIC16C84
    microcontroller by Myke Predko, which I found on the Internet Archive Wayback
    Machine.

I note that all  of the following commands work:
lcdcmd1,2,4,5,6,7,8,12,13,14,15,16,20,24,28
LCDCursor value
LCDHex value
LCDSpace value
Put Line,Column, Character
Locate line, column,
Print string (or byte,word,integer)

Thanks for your continued interest.

[Jack Hoffnung]

Hi Anobium,
I think I may have figured out why custom characters do not work on a 2-wire LCD setup; RW is grounded, thus cannot be used for read/write operations. Am I on the right track?

[Anobium]

That is probably the answer!!
Well done.

I will add to Help File.

We learn something new every day.

:-)