Can defines be changed with port input?

[Archangel]

Hi,Joe

Mhhhh, now, If you DO NOT send data one after the other , but specify WHERE you want it to be written ...

Only 2 lines will be used ...

But YOU MUST Tell PbP you USE a 4 LINES Display ... PbP can't think you only WANT 2 lines ... no DEFINE for unwanted lines !!!

CQFD

Alain.

HI Alain,
The thing is, if you check post #6, I am sending the data in a manner so as to tell PBP where to write each line, I would expect the software to delimit the display to the addresses available only to a 2 line display if it is defined as a 2 line, even with a 4 line display connected, but it displays all 4 lines. Now if I install a 2 line display, and send 4 lines of data as written in post 6, only the lines written for line 1 and line 2 will display. I would have expected the PIC to truncate the third and fourth lines when set to 2 lines, even when connected to a 4 line display. It appears that is not so. So I still have the question, what effect does DEFINE LCD_LINES have on the LCDOUT command?
Regards
JS

[keithdoxey]

OK. I didnt know what the LCD_LINES define actually did so I took a look in PBPPIC14.LIB and located this section of code.....

    if (LCD_BITS == 8)
      if (LCD_LINES == 1)
        movlw   30h             ; 8-bit mode, 1 line, 5x7 font
      else
        movlw   38h             ; 8-bit mode, 2+ lines, 5x7 font
      endif
    else
      if (LCD_LINES == 1)
        movlw   20h             ; 4-bit mode, 1 line, 5x7 font
      else
        movlw   28h             ; 4-bit mode, 2+ lines, 5x7 font
      endif
    endif

The "Function Set" register of the 44780 LCD controller chip has the following bits


D7 = 0
D6 = 0
D5 = 1
D4 = DL
D3 = N
D2 = F
D1 = -
D0 = -

where

DL = DataLength
1 = 8 bits
0 = 4 bits

N = Number of lines
1 = 2(+) lines
0 = 1 line

F = Font
1 = 5x10 dots
0 = 5x8 dots

So looking at the code in the library file, the define is acted upon but is only used to correctly configure the display driver chip for the LCD display connected to it during initialisation.

When you consider that there isnt a define for LCD_CHARS to declare how many characters are on a line then it follows that it cant do anything clever such as work out that you have reached the end of line 1 and move to the start of line 2.

PBP does an awful lot of the hard work for you but there are times when you have to take care of some things yourself.