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Reading from a CFAG12864B

poteau

New member
Hello,

I know it's kind of weird to read from an LCD screen, but the pic I'm using doesn't have a lot of ram, so I can't store all the information on the PIC.

So anyways.. I need to read some information from the LCD screen... I've looked at the timing.. and came up with this code:

LCD_DATA = parallel bus to the LCD
I'm running a 40MHz clock... so wait = 100nS

Code:
ubyte LCD_RD_data(ubyte controller)
{
//returns data from the selected controller
	ubyte data = 0;
	LCD_DATA = 0x0F;
	LCD_DI = high;
	LCD_EN = high;
	LCD_RW = low;
	LCD_CS1 = high;
	LCD_CS2 = high;
	
	wait;
	wait;
	LCD_EN = low;
	wait;
	wait;
	LCD_RW = high;
	if (controller) LCD_CS1 = low;
	else LCD_CS2 = low;
	wait;
	wait;
	LCD_EN = high;
	wait;
	wait;
	data = LCD_DATA;

	wait;
	LCD_EN = low;
	LCD_RW = low;	

	return data;
}
data always comes up as 0x0F as I set it to in the beginning of the procedure.

As always... any help is very much appreciated.. Thanks.
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poteau

New member
doh, I got it!

You are right, I forgot to set it as an input.. but also... I was setting the R/W low like the timing diagram showed... this caused it to write a random character to the screen. I removed it and it works great now!

Just because I couldn't find too much info on this on the forum, I'll put my working code...

Code:
ubyte LCD_RD_data(ubyte controller)
{
//returns data from the selected controller
	ubyte data = 0;

	
	LCD_DI = high;
	LCD_EN = high;
	LCD_RW = high;
	LCD_CS1 = high;
	LCD_CS2 = high;
	TRISD = 0xFF;

	LCD_EN = low;
	if (controller) LCD_CS1 = low;
	else LCD_CS2 = low;
	LCD_EN = high;
	wait_10(1);
	LCD_EN = low;
	data = LCD_DATA;


	LCD_EN = high;
	LCD_RW = low;	
	LCD_CS1 = high;
	LCD_CS2 = high;
	TRISD = 0x00;
	return data;
}
 

poteau

New member
Ok ok... after playing around.. this code would only work the first time.. once I started including it in loops it was giving crappy read backs and screwing up my display.

I was searching around the forum and discovered you need to pulse the enable 2x when reading from the LCD

so HERE is finally code that will work for you!

Code:
ubyte LCD_RD_data(ubyte controller)
{
//returns data from the selected controller
	ubyte data = 0;
	
	TRISD = 0xFF;
	wait_10(5);
	LCD_DI = high;
	LCD_RW = high;

	pulse_enable(controller);
	wait_10(5)
	LCD_EN = high;	
	wait_10(5);
	data = LCD_DATA;
	LCD_EN = low;
	wait_10(5);
	TRISD = 0x00;
	wait_10(5);
	return data;
	
}


void pulse_enable(unsigned char controller)
{
// controller 1 is for the left of screen, controller 2 is for right of screen 
// controller = 0 is for both
	LCD_CS1 = high;
	LCD_CS2 = high;
	switch(controller)
	{
		case 0:
			LCD_CS1 = low;
			LCD_CS2 = low;
			break;
		case 1:
			LCD_CS1 = low;
			break;
		case 2:
			LCD_CS2 = low;
			break;
	}

	LCD_EN = high;
	wait_10(1);
	LCD_EN = low;
	return;
}
 
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