Is This a Bad Driver?

[jpanhalt]

In another thread, I described problems with a $2, 16X2 LCD. All of those problems disappeared when I revised my code and started using a new unit that was received on Friday. Having reached a point of confidence, I reattached the original LCD, and this is what I get:

Hello World was put on one line to force the HD44780U Extension Driver to do something. If two lines are used for the message, it appears OK on the left half of the screen and the right is just the dark rectangles. It looks like a column of pixels is missing from the 4th character in both lines.

Anyone have similar problems? Is there any type of "hard" reset that might help? I suspect I am out $2.

John

 

[Dr_Doggy]

i used those, but mine we rs232 input. had reset, 254-81-0xfe (i think!)
got datasheet?
this one is prolly cooked, and i cant read asm, but have you tried blinky code, ie:
for cnt = 1 to 255
lcd(cnt); delay 100ms;
next

when i got mine, there is a background ram bank bigger than screen , so numbers were getting lost till i tried the scroll commands.

 

[BobW]

Given that the boundary between good and bad occurs at the 8th character, I'd guess that a data or address line has failed somewhere on the display board (not necessarily one of the driver inputs). Possibly a broken trace somewhere?

 

[atferrari]

In another thread, I described problems with a $2, 16X2 LCD. All of those problems disappeared when I revised my code and started using a new unit that was received on Friday. Having reached a point of confidence, I reattached the original LCD, and this is what I get:
View attachment 95539

Hello World was put on one line to force the HD44780U Extension Driver to do something. If two lines are used for the message, it appears OK on the left half of the screen and the right is just the dark rectangles. It looks like a column of pixels is missing from the 4th character in both lines.

Anyone have similar problems? Is there any type of "hard" reset that might help? I suspect I am out $2.

John

Are you using a precise setting to start each line? I recall having funny results because my text was longer than the actual line in the display.

I also recall having a similar experience that brought me to suspect of one particular pin (micro side). Since I forgot details, I just can tell you that in the end I followed one of the three or four best suggestions I ever got. This, by Olin Lathrop in the Microchip forum, many years ago: Set explicitly all SFRs as the manual says they are after a POR. It cured my problem and just in case I do it in all micros, ridiculous as it sounds. (Flaming welcome but ignored.)

BTW, I would test your problematic one with two lines formed by the same char every time, going in sequence from the first to the last possible chars in the list. Those "stupid" tests help to find a pattern in the failure if one could exist.

Buena suerte.

 

[jpanhalt]

I have only 2 of these LCD's. They have exactly the same pinout and presumably the same or functionally same controller. One works and the other doesn't. Same program, same MCU, same breadboard. The "bad" one did work for awhile, and I wasted a lot of time over the weekend with the that LCD thinking it was my code. Much along the lines of BobW's suggestion, I also looked for physical defects in the bad display, but there is not much to see. One of my thoughts was that the elastomeric conductor to the screen may have a defect.

As for the Microchip forum, Olin Lathrop and Dario both emphasize the need to initialize memory and SFR's. I tend to overdo the SFR thing too.

With the working display, a check busy flag routine (WNB) that I had been struggling with worked straight off, and I was able to do some some preliminary timings with ICD3 hardware simulation. Today, I plan to use TMR1 to repeat those tests without the simulation interface and to look at such things as filling the entire screen with characters. The "busy times" that simulation showed were in the range of 28 to 43 usecs. Some of that variation may be due to the relatively slow controller clock. Hopefully, I will get better data today and will update the concurrent thread on displays when I get it.

The main reason for this post was to find out whether there is a "hard" reset like some devices have. My older HP printer, for example, had one in which you held a certain key down while turning the thing on. I assumed that if such existed, it might well not be documented in the datasheet. For the money I have invested in this display, it is not worth messing with any longer, unless there is a simple answer.

Regards, John