Hi everyone..
I have a newbie question..
On the Arduino Mega, can I use Pin 18 and 19 for a screen I2C ?
It's says serial port TX And RX.
What it says is what it does, so no. Pins 20,21 are clearly marked SDA, SCL, being the I2C bus.
Ok,, But I need more than one Screen running, So can I use the other communication ports for the second screen..?
IF the other screen is a serial device, then clearly you can use it on a serial port, but I'm betting it isn't, so no. If it is another I2C display and has, or can be made to have a different address, it can share the bus with the first one - which is what the I2C bus is for. If you intend to have the same display on both, I believe the separate address is unnecessary.
It is a screen with 4 pins - Vcc GND SCL SDA -
Look up software I2C or softI2C. Lots to go through.
Mighty-Eagle:
It is a screen with 4 pins - Vcc GND SCL SDA -
Can you change the 2nd screen's I2C address to be different from the first one's? If so, then you can use the same I2C bus.
neiklot:
Can you change the 2nd screen's I2C address to be different from the first one's? If so, then you can use the same I2C bus.
Well of course you can. That is what I2C is for.
If you want to know how, you have to reveal the secret information. 
Mighty-Eagle:
Ok,, But I need more than one Screen running, So can I use the other communication ports for the second screen..?
Could you provide us a link for your device? Maybe there's a way to change the address by jumper or soldering bridges on the PBC.
No need to be rude when beginner is asking perfectly good questions.
Cheers,
Kari
OK..
how do I link you to my device.. ??
No need to be rude when beginner is asking perfectly good questions.
Paul B's rude reply was to me, and I wasn't even asking the forum a question. The "Can you.." in my question was obviously aimed at the OP, asking him or her if he or she could make such a change. I was essentially posing as a question, what GaryP later said as "Maybe there's a way...".
If I had been asking a question to the forum, I would have asked "Can one...." or "Can I....". In his haste to get in and score a quick point (which seems to be the way many high post count members here work) Paul B may have thought I was the OP.
Mighty-Eagle:
OK..
how do I link you to my device.. ??
Find its page on the net, copy the url, and use the chain icon thingy at the top of the Reply form to put it in your reply as a clickable link.
Mighty-Eagle:
how do I link you to my device.. ??
You need to tell us what sort of "screen" you are talking about? Model number and description, where you got it from? More particularly, give a Web link to the page describing it (preferably an English language one 
)
It says .. Arduino Mega 2560
but this is how it looks..
Mighty-Eagle:
It says .. Arduino Mega 2560
but this is how it looks..
Not the Arduino, the screen
It is a screen with 4 pins - Vcc GND SCL SDA -
LOL
cool..
Screen looks like this..
https://www.dhgate.com/product/lcd1602-i2c-lcd-1602-module-blue-screen-pcf8574/401424857.html
got it from mantech and BangGood..
neiklot:
In his haste to get in and score a quick point (which seems to be the way many high post count members here work) Paul B may have thought I was the OP.
Oh, I am not by any means so easily confused.
No, my reply was to mixed authors, yourself and the OP.
Yes, I did have a point. it is pretty much part of the I2C standard that because I2C devices have defined addresses, they have a mechanism for defining alternate addresses over a small range, usually four or eight. This thread is a classic "XY Problem" as I linked where we have been asked what appear to be "perfectly good questions" but are in fact the wrong question resulting in less-than-useful replies. 
I am simply trying to redirect the conversation toward an actual (optimal) solution.
But my board will not pick up a screen an another location .. Example pins 46 and 47.. would I use the same pins on both screens if they have a different address??
My Uno board can read a screen on pins 18,19 and there is two place for the pins, one one each side..
Look at the bangood pix, the one showing the underside, and use the zoom. You'll see three solderable pairs of pads A0, A1, and A2 next to the SCL pin, which are surely where you set the address. The datasheet will (should?) say which link means what in the address.
OK, now we are cooking!
That "banggood" page put up a fight, but I won!
See the jumper links "A0", "A1", "A2"? These select the I2C address of the display. You can put up to eight of these displays in parallel on the I2C bus, each one having a different setting of these three soldered jumpers.
Suggest you use bperrybap's HD44780 library installed from the IDE Library manager. This will allow you to locate the first "backpack" address; if you tell us what it is, we can tell you how to set other addresses, but for a start, jumping "A0" will either take the address up one if it is even, or down one if it is odd.
I can see that my problem is bigger than what I thought,, I have 8 screens it total and only two have those pins..
this is not good..
..Sad Panda..