4 or 8 interface?

[arash]

What's diffrent between  4 and 8 interface for lcd?

[meax98]

1. The difference between 4 bit and 8 bit operation is that data is sent out as nibbles instead of as one byte.
2. D3-D0 are not used on the LCD when the module is operated in 4-bit mode and D7-D4 are used to transfer
nibbles to/from the LCD module. Note: D7 is the MSB.
3. Commands and data are still 8 bits long, but are transferred as mentioned above as two 4-bit nibbles on data
bus lines D7:4.
3. The most significant nibble should be transferred first, followed by the least significant nibble.
 
You can choose one mode or other. If you use 8-bit mode, than you need more pins (lines), but it's more quickly, then using 4-bit mode.

[Parmin]

4 bit op use longer codes but less pinout. It would also increase the processing time coz it got to send the infos twice in nibble size rather than once in byte.

If you are using a small uP, your pin usage are at premium, you may want to use the 4 bit op.  If you are not limited by pin nos, you should use the 8 bit op because it is more efficient.

Your PCB wiring etc may also determine the type of op you may want to use.

[Timbo]

Not in disagreement with anyone here but I haven't found any reason to use 8 bits, even at 4 Mhz the LCD can update faster than you can see, not to mention 20Mhz even a 4 line 20 char text lcd updates so fast that any quicker would be a blur. I suppose there is the exception but I haven't found an application yet that using all 8 bits would really get me much of anything except burning up 4 more I/O lines on my PIC. - My 2 cents  : )

[Parmin]

Dude,
The 4 bit data breakout requires more lines than the 8 bit ones in program.  Maybe not important if you got plenty of space. but in many jobs, programming space is at premium.  Then the 8 bit lines would save you a few words that may be crucial.
 
LCD update IS faster than your eye can see, but the processor processing time are shared for the display and other stuff.  Ergo, 8 bit is faster to transfer = processor got more time to do other stuff.
 
Then again just my 2 peso, can I swap them with your cents?  

[meax98]

Paramin is right. But if you use uC for home projects and simple automation processes you won't see much differences between 4 and 8 bit LCD mode.
So Timbo, you can use 4-bit connection to LCD and forget 8-bit story.

[Acme]

Hi, I'm looking for an 8-bit initialization routine for Pic-C PCWH.  I've look everywhere but could not find any routines for C language.  Could someone here provide me a working routine for 8 bits  I have pleanty for 4 bit but no 8 bit.
 
Thank's
 
Acme
 
P.S.  Please send me private message

[metal]

Hi

You can find everything you need on CCS forum, its very good, and there are many good guys at C there.

Good luck

[stevetwc]

Hi acme, please take a look at the attached file. It is best to open the file using latest version of MPLAB IDE.
 
Regards.