All the of 16x2 LCD projects I've seen use 4-bit transfer but the displays typically have an additional 4 pins for 8 bit transfer.
I haven't yet seen an example / tutorial that doesn't leave those 4 unused pins floating.
From what I've read, leaving pins floating is widely discouraged, so does it make sense to tie the extra 4 pins to GND?
what problem did you face?
anyway, no one can stop you from connecting free contacts to the ground.
@kolaha Kolaha - No problems at all. Connecting the unused pins to GND will just help with some PCB routing I'm doing.
@mikedb - As far as I can see, there is no mention of connecting D0-3 to anything in that tutorial.
@2112 - So presumably it wouldn't be a problem if they were connected to GND either?
Can you show us a tutorial were the floating pins is connected to GND?
I believe he's saying he hasn't seen an example that does not leave them floating.
That's what I read as well , so would like to see were the unused data pins is ever connected.
@mikedb Maybe I'm using the wrong terminology. I thought if a pin was refered to as "floating", it wasn't electrically connected to anything. So if they're connected to GND, they're not floating?
@2112 Yes, that's what I meant. I'm interested in the implications of connecting those pins to GND, even though I've not seen any suggestion they they should. Would it be good or bad?
Leave them un connected.
There is thousands of tutorial and those pins is never connected.
Unless the data transfer is 8 Bit.
What problems would arise if they were connected?
I can't answer that. I found a note in LiquidCrystal.cpp that states:
// When the display powers up, it is configured as follows:
//
// 1. Display clear
// 2. Function set:
// DL = 1; 8-bit interface data
// N = 0; 1-line display
// F = 0; 5x8 dot character font
// 3. Display on/off control:
// D = 0; Display off
// C = 0; Cursor off
// B = 0; Blinking off
// 4. Entry mode set:
// I/D = 1; Increment by 1
// S = 0; No shift
//
// Note, however, that resetting the Arduino doesn't reset the LCD, so we
// can't assume that it's in that state when a sketch starts (and the
// LiquidCrystal constructor is called).
It's in 8 bit mode until
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);
sets it to 4bit mode. I do not know if it writes to the lower 4 bits between power up and the lcd object.
Sacrifice a display. Connect it as you wish and try it. After 10 or so power and brown out cycles, if the display survives I'll say you're good.
Let us know what happens.
Your worse case would be a brown out where the display resets and the Arduino did not. Simulate that by temporarily removing power from the display while the Arduino stays powered.
Maybe rethink your PCB layout. Why do you think connecting them to ground would be helpful?
In 4 Bit Mode. They are DISSABLED.
so, you have no problem but despite of this you have a wish everything to ground and now your problem is to guess what problem may this cause. very contra productive.
There's an island in the GND fill that i just can't find a way to eliminate without vias and jumpers. If I connect the LCD's unused "8 port" pins (D0-3) to GND, I might be able to eliminate that island.
I'm pretty confident a single jumper wouldnt remotely be a problem - it's just become a challenge to find a way to avoid it.
I've not had time to even try that routing yet, so it might not work, but I fuigred there's no point trying if someone can definitively say it's a bad idea.
No harm in using an air wire if that's what's needed. If you intend to use an air wire, do it with a pads, not a vias.
I assume you have ground planes on both sides. It's a good idea to stitch them together using vias.
Isn't that what we were talking about?
Yes , but the OP still not sure which option to use.
Do what ever with the pins , it does not matter.
Cut them off and use that space on the pcb.