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Strange Behavior with 20*4 LCD (BASIC-Computer with Arduino)

Former Member

I already posted about this issue in this thread, but I think, my issue is different.

I have changed ca. 10-15 lines in the original source code provided by Ben Heck. The 20*4 LCD now outputs Data without line-problems, but the 4 characters in the topright corner are displayed at the beginning of the third line!?

It looks like this: 

                    
TinyBasic
1146 Free.
>10 print "1234567"_

TinyBasic           
1146 Free
>10 print "1234567"
>_

1146 Free.
>10 print "1234567"
>
>_

>10 print "12345
>
>7"
>_

in the fourth frame, after pressing LF, until the entered command goes up to the first line, only the left 16 chars are shown (the rest are blanked out), and the other 4 are in the third line, although the 17th is overwritten by the cursor > (in fact, up to all 4 could be overwritten if something would be written in this line)

Does anyone knows how to fix this? I am desperately trying to figure this out.

I marked the changes I made in the source code in the link in the first line in this post. I don't know if I am allowed to post the script here.

 

Thanks!

  • 0

    Some RAM is set aside as "screen memory" in that code. It is then mapped to the display.

     

    Check that enough has been allocated, since youre display is larger than the one I used.

  • 0 in reply to benheck

    First of all, thanks for responding!

     

    I initially changed int screenMem[72]; (at the beginning of the script) to 76, which took away most display errors. I now tried to increase this array to 80, then 100, but it did not work. When I increase it even more, (103 or more), nothing is displayed at all.

    I also figured out that your lcdChar () function (called by outchar) overlaps, but changing anything only results in a very strange display behaviour (all the text is in wrong places, like so: http://www.element14.com/community/message/81178#81178).

     

    1574
    		for (int xg = 0 ; xg < 20 ; xg++) {
    1575
    		screenMem[0 + xg] = screenMem[40 + xg];00-19 -> 40-59
    1576
    		 screenMem[40 + xg] = screenMem[20 + xg];  40-59 -> 20-39
    1577
    		 screenMem[20 + xg] = screenMem[56 + xg];20-39 -> 56-75
    1578
    		 screenMem[56 + xg] = 32;56-75

     

    When I increase screenMem[xy], the "bytes free" (shown at the beginning, Tinybasic - 1146 free), does not get smaller. Do I need to manually decrease that value? if yes, where?

     

    Thanks.

  • 0 in reply to Former Member

    ScreenMem is divided into 4 lines. Should be 80 total (20 times 4)

     

    As for free space, check the beginning of the code, it might manually reserve the free space, or use a large array as its RAM.

     

    It's been over a year since I hacked that Tiny BASIC code, I don't really remember all that I did.

     

    At a certain point, wouldn't it just be easier to use the original sized screen?

  • 0 in reply to benheck

    I'll check that when I'm home again next week. It is not *that* important, it just looks hgrrrrr!! image I can live with it, if I can't get it to work!

     

     

    Thanks!

  • 0

    The chip that drives the LCD has a characters memory of 4 lines and 40 characters for each line.

    That is happening because this chip is used in a variety of LCD screens.

    Yours is only 20 characters long for each line so you can write the first 20 letters and then you have to change line by adding + 21 because the first memory address is the zero "0" not the 1.

    at least as far as I can remember the 40 th by number memory address must probably be the first character of the

    SECOND LINE.

    So the first character of the third line is the 80th by DECIMAL NUMBER memory address.

    And the forth's line first memory DECIMAL number is 120.

    So the last memory address is 159 decimal.

    The program should have 4 loops of the For (  ) {  } each one loading an array of characters with the size of 19

    because arrays begin too from 0 not 1 because in a binary system the very first state is the zero in all of it's bits.

     

    allways search for the manual of the chip you are trying to use in a circuit board.

     

    I think I helped you a lot but try to look at the chips manual for any different numerical assignment of the addresses. But I believe I remember right the way this 30+ years old chip in the LCD DISPLAY functions.

     

    Message was edited by: Gerasimos Kokkinos

  • 0 in reply to benheck

    Xg ++ should be put inside the loop and not in the declaration of the For (  ){ }

    That is because your variable enters the loop already added by one "1" so the loop begins with your variable higher by one more than you expected to be.

    So instead of beginning with zero it begins with one so you have 19 repeats not 20.

    All of my posts refer to the C++ language ,for the basic as language adjust accordingly.


     

    Message was edited by: Gerasimos Kokkinos