Improvements to the LiquidCrystal library

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"40x4 LCDs
I added support for an LCD of 4 LInes and 40 characters. I think that if 24x4, 
32x4 LCDs exist, 
they would also work with the software as I have modified it although I have 
not had the 
opportunity to test that. The 40x4 LCD (and any HD44780 based LCD with between 
81 and 160 
characters) will have 2 enable lines. To use an LCD with 4 lines and 40 columns 
you would 
declare your LiquidCrystal object as:
LiquidCrystal lcd(RS,RW,Enable1,Enable2,  data3,data2,data1,data0); at this 
time I don’t support 
8 data lines nor do I support eliminating the RW line in this option.Then in 
the setup function 
you would call:
lcd.begin(40,4);

Linewrap
When you declare the dimensions of the LCD in your begin call, the 
LiquidCrystal library 
remembers how long the lines are. Now when it reaches the end of line 1, text 
wraps onto line 2 
(not line 3 as previously). 

16x4 LCDs
The begin statement also correctly positions text at the beginning of the line 
on 16x4 (and 40x4) 
LCDs, which were not correctly handled before.

setCursor
In the past setCursor selected a location in the HD44780’s RAM not actually a 
screen location. If 
you use any of the commands that shift the display left or right with the 
previous routines, then 
setCursor and print, text appears in an unexpected location on the screen. With 
the new 
software,  if you call either scrollDisplayLeft() or scrollDisplayRight(), the 
LiquidCrystal package 
keeps track of the relationship between RAM and the LCD so that setCursor 
coordinates are 
pegged to a specific spot on the screen, rather than a spot in RAM. The sotware 
does not handle 
autoScroll, however. Call home() after autoScroll to restore the expected 
relationship between 
setCursor and the LCD screen.

Testing the LCD Busy Flag
Previous versions of LiquidCrystal always used timed delays on the Arduino side 
of the interface 
to give the LCD module enough time to complete its operation. This version 
still does that if you 
tie the RW pin to ground and do not tell LiquidCrystal what that pin number is. 
If you do specify 
RW now, however, the software will poll the busy flag on the LCD module. 
Arduino operations 
may thus overlap LCD operations and potentially things may go a little faster. 

Crazy 8 Addressing
16x1 LCDs often have an unusual address layout; these modules often have two 8 
character 
halves and work best with this software if you declare them as lcd.begin(8,2); 
if you do that, then 
you can print(“abcdefghilklmno”); and have all the characters appear as you 
would like across the 
screen. If you use any of the scrolling commands, the bizarre addressing of 
these modules will 
manifest itself. For details follow the _LCD Addressing_ link at 
web.alfredstate.edu/weimandn 

Disadvantages
The two real disadvantages I can see to the changes I have made are:

The code is longer than before. Much of the increase is in checkLcdBusyFlag() 
and this could be 
fairly easily replaced with delayMicroseconds(100);

2. The possibility that someone with a little 16x2 LCD is using the 
scrollDisplayLeft() or 
scrollDisplayRight() instructions to move data across the screen, but wants to 
write the data 40 
characters at a time with a print statement. This version really does not let 
the user write data to 
the HD44780 DDRAM which is not visible. To accomplish a scrolling display with 
40 characters 
per line, you would now need to write 16 characters, scroll the display, write 
a little more and so 
on.

There are going to be some incompatibilities between code that assumed that 
line 1 wrapped 
onto line 3, etc."

Original issue reported on code.google.com by dmel...@gmail.com on 1 Feb 2010 at 4:37

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Original comment by dmel...@gmail.com on 1 Feb 2010 at 4:37

• Added labels: Milestone-0019

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There are several versions that are available at 
http://code.google.com/p/liquidcrystal440/downloads/list
My recommendation for -19 is the last version ('4bit'). It fixes one bug that I 
think is in the others (Paul Stoffregen found it reading the code, it only 
shows up when the 2nd enable line on the 40x4 LCDs is attached to pin 0). It 
has longer delays that support (rare) LCDs that work slower than the vast 
majority. I think that is desirable to avoid problems for the few who end up 
using those slower LCDs.

The places that might be controversial (vis a vis -19) it seems to me are:
in LiquidCrystal.h there is a one line inline fcn overriding (); that supports 
the syntax lcd(15,1) to mean the same as lcd.setCursor(15,1) and is intended to 
complement use of Mikal Hart's Streaming library. It is 'weightless'--there is 
no additional code generated to support it.

The userbusy versions of the API. These are complex to use and explain. They 
add a little performance advantage which might be worthwhile in certain 
time-critical situations. It is very lightweight--the code to support it is 
almost all written by the user, in the user sketch, but not 'weightless'; there 
are 2 versions of the initial call to instatiate the LiquidCrystal object and a 
few lines of code to call the userbusy routine.

Original comment by johnrain...@gmail.com on 8 Jul 2010 at 10:24

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Any chance you can split out these improvements into separate patches and 
issues?  For example, using the R/W pin (if supplied) to lower wait times would 
be a good, straightforward change, and the auto-wrapping of text could be nice 
too.  Also, supporting 16x1 LCDs in a more intuitive way would be good.  40x4 
LCDs don't seem that common (at least, SparkFun doesn't sell any), so maybe 
it's not needed in the core library?  

Original comment by dmel...@gmail.com on 10 Jul 2010 at 8:45

• Removed labels: Milestone-0019

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http://www.nkcelectronics.com/character-lcd-module-40x4-yellowgr404.html

I will try to get a version that does not support the 40x4 and 27x4 displays 
tested  and posted in the next 48-72 hrs. 

Original comment by johnrain...@gmail.com on 18 Jul 2010 at 12:47

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I posted a version that eliminates 40x4 LCD support and the UserBusy test on 
the google code link above. I hope this works for you. It certainly simplifies 
parts of the code.

I do know that I wasn't the first to implement 40x4 support, but it had been 
done with much earlier versions of the code base that did not work nearly so 
well.

The code needs appropriate copyright notices added. Please do that.

I put comments in both the .cpp and .h file around lines I think should be 
eliminated when the name changes to LCD in 1.0

Original comment by johnrain...@gmail.com on 18 Jul 2010 at 9:58

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Yet another solution for 40x4 displays. Use inheritance to support 40x4 
displays instead of a big "can do everything" library. The following patch 
enables inheritance on the lcd library: 
https://github.com/arduino/Arduino/pull/87 and 
https://github.com/manfredjonsson/LiquidCrystalAddons shows possible usages 
including 40x4 support.

Original comment by mmmjons...@gmail.com on 2 Jun 2012 at 1:04