Garbled LCD screens

[Roxy]

One would think, but no. "Initialization" involves sending a particular sequence of commands to the display module, with specific timing constraints on the transfers. That's all my "fix" is doing - periodically reinitializing the display by going through that command sequence again. There's a bit of delay in doing this, but I don't notice it on my printer. If I understand Marlin right, any printing going on should be handled in interrupts, so the additional time spent reinitializing the display shouldn't affect anything.

OK... But here is the next question... If you are sending some 'Initialization' sequence, does that involve sending it bytes of data to give it commands? Because if it does and the LCD Panel is out of sync, aren't the 'Initialization Commands' scrambled?

[printbus]

OK... But here is the next question... If you are sending some 'Initialization' sequence, does that involve sending it bytes of data to give it commands? Because if it does and the LCD Panel is out of sync, aren't the 'Initialization Commands' scrambled?

Aw, man. I guess I should have known better than to gloss over details. State of the RS (register select) pin when the E pin is strobed is how the LCD module differentiates commands from data. At the start of the initialization sequence the LCD module doesn't know if the transfers will be 4-bit or 8-bit, but the first commands used only have four valid bits, and the others are don't care. So, the multiple-nibble synchronization problem can't occur on those first commands.

EDIT: I'd summarize the interface these modules have as fairly clunky by today's standards. I don't know how long the interface has been out there - I bought my first module off the surplus market in 2004, so I'm guessing it's been out there 15 years or so.