Matthew Mucker wrote:
> All,
>
> I've been debugging this problem for weeks and haven't found where my error
> is, so I'm turning to the list for help. I'm trying to drive a Hitachi 44780
> LCD module in 4-bit mode from a PIC chip.
>   
Are you sure you have a "real" 44780 ?
Anyway after using a lot of displays without any problems,
I got a VARITRONIX type which gave a lots of trouble.
An extra delay solved the problem, see code below.

success,
Stef Mientki



|-- <Version: 1.2    ,01-09-2004, Stef Mientki
--    - Extra delay in Init procedure, after 4-bits setting, 
--      needed for VARITRONIX MDLS-16268-series
--        Problem was a uncomplete reset, after which the total behaviour was instable

||
const _HD44780_short_delay = 5|

|
||procedure LCD_init is
  -- if multiplexed IO-pins, these values will be set just before sending
  if ! HD44780_multiplexed_output then
    HD44780_b4_pin        = low
    HD44780_b5_pin        = low
    HD44780_b6_pin        = low
    HD44780_b7_pin        = low
    HD44780_DataCmd_pin   = low

    HD44780_b4_direction  = output
    HD44780_b5_direction  = output
    HD44780_b6_direction  = output
    HD44780_b7_direction  = output
    HD44780_DataCmd_direction = output
  end if

  HD44780_Enable_pin       = low
  HD44780_Enable_direction = output

  delay_1mS ( 40 )                      -- even long enough for Vcc as low as 2.7V
  HD44780_DataCmd_pin = low                 -- select command
  _HD44780_write_low_nibble ( 0b_0011 ) -- first init
  delay_1mS ( 5 )                       -- extra delay
  _HD44780_write_low_nibble ( 0b_0011 ) -- second init
  delay_10uS( 10 )                      -- extra delay
  _HD44780_write_low_nibble ( 0b_0011 ) -- third init

  _HD44780_write_low_nibble ( 0b_0010 ) -- set 4-bit interface
  delay_10uS( _HD44780_short_delay )    -- FOR SOME DISPLAYS (VARITRONIX) required delay
  _HD44780_Command( 0b_0010_1000 )      -- two lines, 5x7 (high nibble)
  _HD44780_Command( 0b_0000_1111 )      -- display on, cursor on, blink on
  _HD44780_Command( 0b_0000_0001 )      -- clear display
  _HD44780_Command( 0b_0000_0110 )      -- increment and no shift

  -- now display version of this lib
  delay_1ms(100)
  LCD_char_pos ( "V", 1)
  LCD_char_pos ( " ", 2)
  LCD_char_pos ( "1", 3)
  LCD_char_pos ( ".", 4)
  LCD_char_pos ( "4", 5)
end procedure
|

> I have my PIC 16F628 connected to the LCD module as follows:
>
> RB4 --> LCD_E
> RB3 --> LCD_RS
> RA0 --> LCD_D4
> RA1 --> LCD_D5
> RA2 --> LCD_D6
> RA3 --> LCD_D7
>
> I have tested each of these outputs and verified that I can write a logic
> '1' or '0' and get the expected voltage.
>
> I've used Myke Predko's page (www.myke.com/lcd.htm) as my main reference.
>
> According to MPLAB SIM, my code is writing the following when the LCD_E line
> is blipped:
>
> 			LCD
> 			DATA	LCD
> TIME			7654	RS	notes
>
> 0			0011	0	send 0x03, wait 5msec
> 5.1964		0011	0	send 0x03, wait 160 usec
> 5.5218		0011	0	send 0x03 a third time, wait 160 usec
> 5.8472		0010	0	Enable 4-bit mode (following commands are
> two nybbles)
> 6.0126		0010	0
> 6.1766		1000	0	00101000: 4-bit mode, 2 line display, 5x7
> font
> 6.3248		0000	0
> 6.5068		1000	0	00001000: disp. Off, cursor off, blink off
> 6.6730		0000	0
> 6.8370		0001	0	00000001: clear display, wait
> 12.0356		0000	0
> 12.1996		0110	0	00000110: increment cursor/no shift
> 12.3658		0000	0
> 12.5298		1100	0	00001100: display on, cursor off, blink off
> 12.6968		0000	0	
> 12.8608		0010	0	00000010: home cursor
> 18.0618		0101	1
> 18.2258		0111	1	Letter 'W', first character to be displayed
>
> The LCD doesn't seem to initialize and for sure my characters aren't being
> displayed. I'm getting quite frustrated with this project. I'm hoping
> someone out there can spot the error of my ways for me and help me get back
> on the straight and narrow.
>
> Thanks,
>
> -Matt
>
>   

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