HD44780 and floating RW pin

In the simulator, HD44780 works fine with floating RW pin. In reality, it should be low or high, otherwise the state is undefined. I would have to test my LCD behavior, but I'm almost certain it will not be functional if the pin floating...

And another thing: grounding one or all D0-D3 pins will probably prevent correct initialization in 4-bit mode. And similar... Should be tested on real device, but in theory, these should be problematic parts.

In the simulator, HD44780 works fine with floating RW pin. In reality, it should be low or high, otherwise the state is undefined. I would have to test my LCD behavior, but I'm almost certain it will not be functional if the pin floating...

Yes, in the simulator unconnected pins read low.
Simulating the behavior of floating pins is out of the scope of this simulator by now.

And another thing: grounding one or all D0-D3 pins will probably prevent correct initialization in 4-bit mode. And similar... Should be tested on real device, but in theory, these should be problematic parts.

I don't understand this one.

For the second one, I have read somewhere that if use 4-bit mode, grounding unused pins D0-D3 may result in LCD initialization failure. Never tested this. Or, perhaps, that was related to another controller...

For the second one, I have read somewhere that if use 4-bit mode, grounding unused pins D0-D3 may result in LCD initialization failure. Never tested this. Or, perhaps, that was related to another controller...

I didn't know about this.
Looks like RS, RW, D0-D7 have pullups, so if unconnected they should read High.
Then RW unconnected is not floating, it's High, so it's wrong in simulide.

Perhaps for original HD44780, but for cheaper Chinese "clones", may be different...

Though, with these Chinese clones I had a problem during initialization, because of timing issue - they are much slower than original controller. I have barely found datasheet for that particular model from manufacturer, then I have noticed differences.

Perhaps is similar issue having pull ups or not on some pins.

BTW, the LCD model I have, have "ST7066U or compatible" by datasheet (it is covered COB by epoxy). Thus, it is not quite clear, it should be mostly compatible with HD44780...

BTW, another thing in simulator is to show squares when power is on, until initialization finish correctly on original HD44780. On some clones that is not present...

Perhaps for original HD44780, but for cheaper Chinese "clones", may be different...

Well.. we should stick to original HD44780 datasheet.

BTW, another thing in simulator is to show squares when power is on, until initialization finish correctly on original HD44780.

Ok, I will have a look to this.

Pullups implemented at Rev 1081.

Now RW needs to be driven, floating RW will not work.

Seems that now LCD behavior is unstable. Previous project I tested with now randomly works, randomly show garbage or doesn't work at all on multiple power button hits...

This was in 4-bit LCD mode. Though, 8-bit mode doesn't work at all.

BTW, I have no idea how to attach here zip file with sim file and source...

Seems that now LCD behavior is unstable. Previous project I tested with now randomly works, randomly show garbage or doesn't work at all on multiple power button hits...

This was in 4-bit LCD mode. Though, 8-bit mode doesn't work at all.

I noticed, but I think that's a problem with AVRs.
I need some more testing to find the cause.

BTW, I have no idea how to attach here zip file with sim file and source...

https://simulide.forumotion.com/t383-how-to-add-pictures-and-attachnents-to-your-posts

It should work fine with AVRs, both 4-bit and 8-bit. Perhaps some modules may be disable, but never had some issue with.

Funny, I did not seen "Attach file" extension, it is on other half of the screen....

Same than in my test: first time works, next times doesn't.

It is realted with RS input, first time it goes low at simulation start, next times it doesn't, even if not connected to LCD.
So I'm almost sure it is an AVR Pin issue.

Disable 8-bit and use 4-bit - first time may work when app is opened, second time will show garbage or nothing at all...

Some init values in simulator may missing, or timing is not correct...

Original driver auto-initialization on power on is in 8-bit, meaning it should work without init sequence...

First I have to solve the problem with AVR Pin, without this is not possible to test the LCD with AVRs.
HD44780 is working OK with PICs.

Problem with AVR Pin solved at Rev 1094.