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NHD-0240A2 Can't write to location 30 in either row

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I have a 2 row 40 character display and I don't know what's going on here but I can't write a single character to location 30 in either row 1 or 2 addresses 9F & DF.  I can write strings of characters but not one character at a time to those locations.  I can write single characters to other addresses but not those two.  I have another NH display that I tried and I have the same problem with that display also.

Any Ideas, Thank You

Would it be possible to get a picture of your display and the code you are using?

I would like to see if we can recreate the same problem.

Here is the photo.  The problem is the character after the #4 in the row 2.  I found this problem while testing.

I am trying to make the characters (b thru h) in row 1 change from upper & lower case if an input is active or not.

This code is not complete!  There are parts of it that are not being used.

The LCD section is run from CALLs on page 3

The problem I am Having is on page 6, LCD_Upper & LCD_Lower address DF or row 1 address 9F.  If I use any other addresses it will work.

[Solved] I couldn't figure out why only certain parts of the display acted up and others did not.

So, here is what I did.  I bought a display from a different manufacturer and that was worse yet!  Then I knew it had to be something in my code.  The first thing I did was slow the clock speed down to 500 kHz and then it worked fine so I went up to 1MHz and the problems came back  Then I knew it was timing.  I added time delays in until I found one the solved the problem and I found it in my E pulse.  I had one NOP in there and that wasn't enough, I tried 3 NOPs and still that wasn't enough.  To make a long story short I finally got it to 5ms and every thing was ok after that.

I never got any suggestions so maybe I was not the only one that was stumped.


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