Garbled LCD screens

[Roxy]

To clarify for the interested, the interface involved with at least these display panels consists of six dedicated pins on the Arduino processor. i2c isn't involved. SPI is ran to the panel on at least the RepRapDiscount smart controller, but it is used with the SD card, not the LCD module. The six pins consist of an enable, a register select, and four parallel data lines. Low level operations involved with setting the data lines and toggling the enable and register select pins are accomplished through Arduino LiquidCrystal library functions. Marlin code takes care of higher level stuff like menu structure.

It could be there's more than one thing going on, but static discharge is definitely a way I've seen my display mess up.

I don't remember why I was thinking i^2c was used. I think I was looking at some of the smaller Arduino boards that had less I/O pins and that ended up being how a given LCD Panel worked with it. Your explanation about each character being transferred as 2 nibbles is helpful. I think what you are saying is there is no signalling to the LCD Panel to tell it which 1/2 of the character it is receiving. It just starts in the right state and every other nibble that is transferred to it is the start of another character. That seems like it is just asking to get out of phase if anything unexpected happens.

It would seem they should have some way to reset the panel and get it to a known state???

Another question is this: Since a lot of the LCD Panels use the same support chip, does this happen equally often with all of them? Or does it mostly happen with specific Arduino boards? Is there some combination that is more prone to the display getting out of sync? Is it at all related to how clean the power is? I know my PrintrBoard had trouble powering the Servo for Auto Bed Leveling. Do the LCD Display boards grab a lot of power from the Arduino board?

The reason for the questions is if the root cause of the LCD Panel getting out of sync is because of missing or double clocking of the nibbles... It would seem slowing that down and making sure there are nice clean edges to the Enable and Select lines after the data is stable would help. Right? But if the corruption happens because of noisy power or something else, the solution will be doing things to clean that up.

UPDATE: And the more I look at this, the more I don't know. Pulling up this link: http://www.reprap.org/wiki/RAMPS_LCD it shows how to build the LCD Panel and it claims it is enabled by taking the comments off of the #define ULTRA_LCD line. But when you look at their directions, they are saying the LCD Panel has 8 data lines and they only hook up 4 of them???? It would seem they should have some 'illegal' combination of RS, R/W and Enable that causes the display chip to reset????

Oh and here is at least one example of an LCD Panel using i^2c: Check out: http://blog.reprap.org/2008/10/new-b...oller-v10.html That must be why I was thinking they were using i^2c in general for this stuff.