TMS320F28075 LCD Display 4bit Mode(power on/off issue)

Hello Vivek,

I have interfaced using GPIO's sending data in parallel way.

For 8 bit mode 8 GPIO'S for D0 to D7 (data lines) and 2 GPIO for RS and Enable pin each,R/W pin is grounded (Total GPIO'S - 10)

For 4 bit mode 4 GPIO's for D4 to D7 (data lines) and 2 GPIO for RS and  Enable pin each ,R/W pin is grounded (Total GPIO'S - 6)

Regards,

Sanath Rai

Hello Gautam,

I have followed the same structure and its working fine for both 8bit and even for 4 bit mode.

only issue is in 4 bit mode when i turn off the controller board and on it again nothing appears on display.

Regards,

Sanath Rai 

i have grounded remaining 4 data lines.

Tried powering up the LCD from External supply.
Here's the scenario:

1.First we powered the LCD display.
2. Powered on the controller.Display didn't work.
3.Again Micro controller powered on and off keeping the LCD display on by external supply.
4.The Display worked.

2nd scenario

1. Micro controller turned on.

2.External Supply for Display on.

3.Display wont work.

sanath rai said:

1.First we powered the LCD display.
2. Powered on the controller.Display didn't work.
3.Again Micro controller powered on and off keeping the LCD display on by external supply.
4.The Display worked.

So here... even if you do multiple times controller reset, the LCD displays right (apart from the first time)? Can you give delays while initializing LCD... I mean after every initialize command in LCDinit() function. I somehow feel the LCD initialization is not happening properly.

sanath rai said:

2nd scenario

1. Micro controller turned on.

2.External Supply for Display on.

3.Display wont work.

The 2nd power sequencing doesn't make any sense :)

Hi Santha,

For 8 bit mode 8 GPIO'S for D0 to D7 (data lines) and 2 GPIO for RS and Enable pin each,R/W pin is grounded (Total GPIO'S - 10)

For 4 bit mode 4 GPIO's for D4 to D7 (data lines) and 2 GPIO for RS and  Enable pin each ,R/W pin is grounded (Total GPIO'S - 6)

What GPIO pins (e.g. GPIO15 or GPIO21 ...) you are using in both case?

Regards,

Vivek Singh

For 8 bit mode GPIOs are Gpio 8,9,10,11,12,1,4,3 for data lines,  Gpio16,17 for RS and Enable redpectively

For 4 bit mode GPIOs are Gpio 12,1,4,3,Gpio 16,17 for RS and Enable respectively

Regards,

Sanath Rai

Is this a fixed PCB or can we play with GPIOs? Have you tried doing so?

No its not fixed,

i have already changed GPIO'S and checked with different IOs.

Regards,

Sanath Rai

Can you try this: (Use the same commands and delays are in millisecs)

void lcd_init() {
    _delay_ms(50); 			// wait for VDD to rise
    lcd_write_nibble(0x3);
    _delay_ms(5);
    lcd_write_nibble(0x3);
    _delay_ms(1);
    lcd_write_nibble(0x2); 	// 4-bit mode
    _delay_ms(1);

    lcd_write_byte(0x28); 	// 2 lines, normal font
    _delay_ms(1);
    lcd_write_byte(0xC); 	// display on
    _delay_ms(1);
    lcd_write_byte(1);		 // display clear
    _delay_ms(1);
    lcd_write_byte(0x6);  	// increment, don't shift
    _delay_ms(1);    
}

Seems pretty odd and I'm running out of ideas :)

sanath rai said:

Infact with your given LCDinit function when i comment the first 3 commands only its displaying ,
but the old reset issue continues.

The first 3 commands are a 4-bit/nibble write. So if you're doing a byte write you need to write 0x03, 0x03 and 0x02 respectively.

ya its odd.

if i do a  reset ie: make XRS pin low in hardware the display works.
so i am planning to introduce a soft reset in the beggining of my code.
how about watchdog reset?

EALLOW;
WdRegs.WDCR.all = 0x0094;
EDIS;

Regards,
Sanath Rai

sanath rai said:

how to reset only for the 1st time using watch dog?

I'd done this exercise once... here you need an EEPROM. 1st time you boot, you should not feed the watchdog -> Store 1 in EEPROM. Next time you boot (after watchdog reset), if 1 is already stored in EEPROM, you'll start feeding the Watchdog henceforth -> Store 2 in EEPROM. Those were the crazy days lol :)

Regards,

Gautam