[sdiy] LCD hot rodding

Roman Sowa modular at go2.pl
Tue Apr 9 10:04:50 CEST 2024



W dniu 2024-04-08 o 16:35, mark verbos pisze:
> 
> One row. Controlling the contrast just dimmed the black boxes. Looking at the data lines, everything looks pretty curved on the rise. In the schematic, I notice that each line going to the display has a 10k pull up and a 10k pull down. Could this be the problem?
> 
> 

 From what I can tell looking at blurry schematics, display is not 
buffered but hooked to databus so you will see all the traffic. Curved 
edges happen when data bus is in hi-Z state.
Set trigger of your scope to rising edge of E signal at the display and 
then look at all the signals, especially RS.

Why it has every input tied to 2 resistors is mystery to me. I'd rather 
put puull up or pull downs here, but not both! Anyway, the most 
important line - E is driven directly from logic gate, so it should be OK.
Timing was mentioned few times here, and that's also one good reason to 
prevent it from working. RegisterSelect of LCD is driven directly from 
A0 address line, so it ma cause problems.
It all looks like the engineers did their best to make it work with this 
particular LCD model, trying hard to finish it before NAMM or something 
back then.

Roman


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