How flexible is the Flex LCD Driver

crystal_lattice · Joined: 13 Jun 2006 Posts: 164

I have a PCB design on which i can allocate the first nibble of port A (A0-A3) to the data lines of the LCD but this complicates other traces elsewhere.

So my question is, can the flex driver be used on 'random' pins or does the data lines have to be a nibble of a port. If random then i can simplify my layout by using the closest pins available. I've searched the Code lib and all the implementations i've seen have a port nibble allocated to the LCD dat lines, either the upper or lower.

I also understand that the Flex driver uses more ram, could anyone give a figure of how much (for a 18f4620)

Just another quick question, from what i understand the R/W and EN pins can be fixed(tied to Vdd/Vss), when the LCD is only to be written to and always ON/Enabled?

EDIT: I've just stumbled upon a post from PCM:
http://www.ccsinfo.com/forum/viewtopic.php?t=24661

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

It can use random pins. However, if the MCLR pin is disabled and used
as RE3, it's an input-only pin. Don't use it for the LCD.

Any additional RAM usage, if such exists, would be a slight amount.
Given that you've got 3986 bytes in the 18F4620, I wouldn't even
worry about it.

The EN signal is a strobe that initiates a read or write operation.
This is clearly stated in the HD44780 data sheet. It can't be tied high.

The Flex driver explains how to configure it for a 6-pin interface
by connecting R/W to GND and commenting out a #define statement.
It's explained in the comments in the link.

I suggest that you make a breadboard of the PIC and the LCD and
test it before you design a printed circuit board.

crystal_lattice · Joined: 13 Jun 2006 Posts: 164

Thanx for clarifying that PCM, my datasheet for my lcd (Topway) is not very clear on the 'function' of the EN pin hence the confusion. The ram usage is a bit of a concern as i'm also running a FAT FS on the pic, which eats more than half the ram...

The breadboard idea is being delayed due to another sampled pic which has not arrived yet... but yes that would be the best route

Yes, i saw your post regarding the comenting out of the R/W #define... and the guy whom wanted to try his own thing...!

Just as an somewhat off the topic question, my understanding is that the other 'ICD' pins (PGM, etc) can be used as outputs only, eg driving the EN pin or a LED?