Powertip 20x4 LCD ST7066U

[Edward]

I am using Powertip 20x4 LCD ST7066U and observed a percular problem.

I programmed the microchip usign ICD2 USB.
Upon ready, I pluck out the cable and the LCD works.

However, when I power off the device and power it on again, the LCD doesn't work.

The attached is my LCD code.

struct lcd_pin_map { // This structure is overlayed
BOOLEAN enable; // on to an I/O port to gain
BOOLEAN rs; // access to the LCD pins.
BOOLEAN rw; // The bits are allocated from
BOOLEAN unused; // low order up. ENABLE will
int data : 4; // be pin D0.
} lcd;

#byte lcd = 0xF83 // This puts the entire structure
// on to port D
#define lcd_type 2 // 0=5x7, 1=5x10, 2=2 lines
#define lcd_line_1 0x00 // LCD RAM address for the 1st line
#define lcd_line_2 0x40 // LCD RAM address for the 2nd line
#define lcd_line_3 0x14 // LCD RAM address for the 3rd line
#define lcd_line_4 0x54 // LCD RAM address for the 4th line


BYTE const LCD_INIT_STRING[5] = {0x20 | (lcd_type << 2),0x20 | (lcd_type << 2), 0xc , 1, 6};


// These bytes need to be sent to the LCD
// to start it up.


// The following are used for setting
// the I/O port direction register.

struct lcd_pin_map const LCD_WRITE = {0,0,0,0,0}; // For write mode all pins are out
struct lcd_pin_map const LCD_READ = {0,0,0,0,15}; // For read mode data pins are in

BYTE lcd_read_byte() {
BYTE low,high;
set_tris_d(LCD_READ);
lcd.rw = 1;
delay_cycles(1);
lcd.enable = 1;
delay_cycles(1);
high = lcd.data;
lcd.enable = 0;
delay_cycles(1);
lcd.enable = 1;
delay_us(1);
low = lcd.data;
lcd.enable = 0;
set_tris_d(LCD_WRITE);
return( (high<<4) | low);
}


void lcd_send_nibble( BYTE n ) {
lcd.data = n;
delay_cycles(1);
lcd.enable = 1;
delay_us(40);
lcd.enable = 0;
}


void lcd_send_byte( BYTE address, BYTE n ) {

lcd.rs = 0;
while ( bit_test(lcd_read_byte(),7) );
lcd.rs = address;
delay_cycles(1);
lcd.rw = 0;
delay_cycles(1);
lcd.enable = 0;
lcd_send_nibble(n >> 4);
lcd_send_nibble(n & 0xf);
}

void lcd_send_byte_init( BYTE n ) {

lcd.rs = 0;
delay_cycles(1);
lcd.rw = 0;
delay_cycles(1);
lcd.enable = 0;
lcd_send_nibble(n >> 4);
lcd_send_nibble(n & 0xf);
}


void lcd_init() {
BYTE i;
set_tris_d(LCD_WRITE);
delay_ms(200);
lcd.rs = 0;
lcd.rw = 0;
lcd.enable = 0;
lcd_send_nibble(3);
for(i=0;i<=4;++i)
lcd_send_byte_init(LCD_INIT_STRING[i]);

}


void lcd_gotoxy( BYTE x, BYTE y) {
BYTE address;

switch (y)
{
case 1 : address=lcd_line_1; break;
case 2 : address=lcd_line_2; break;
case 3 : address=lcd_line_3; break;
case 4 : address=lcd_line_4; break;
default : address=lcd_line_1; break;
}
address += x;

lcd_send_byte(0,0x80|address);
}

void lcd_putc( char c) {
;
switch (c)
{
case '\q' : lcd_send_byte(0,1);delay_ms(2); break; // clearscreen
case '\1' : lcd_gotoxy(0,1); break; // goto beginning of line 1
case '\2' : lcd_gotoxy(0,2); break;
case '\3' : lcd_gotoxy(0,3); break;
case '\4' : lcd_gotoxy(0,4); break;
case '\b' : lcd_send_byte(0,0x10); break; // backspace
default : lcd_send_byte(1,c); break; // send the character
}
}

char lcd_getc( BYTE x, BYTE y) {
char value;
lcd_gotoxy(x,y);
lcd.rs=1;
value = lcd_read_byte();
lcd.rs=0;
return(value);
}


Hope someone can help.

[Ttelmah]

Try setting the port pins to a 'known' state (idle, with the CCD deselected), at the start of your main function.
What you describe, is fairly common, where the newly powered chip, has the lines floating, and these go to state where perhaps the chip is selected, then when the first chip select is sent, this is not 'seen', and the first part of the initialisation is then not seen by the LCD controller. When you first program the chip, the behaviour is often not quite the same as the 'power on' state, leading to this type of difference.

Best Wishes

[Guest]

Forgive me, but how to set the port pins, in this case port D to a known state. Thanks for the reply.

[Edward]

I am still figuring out

Try setting the port pins to a 'known' state (idle, with the CCD deselected), at the start of your main function

Anyone kindly help?

[Ttelmah]

[PCM programmer]

[Edward]

Thanks for the reply Ttelmah, I will try 'output_d(255)'

I am using is Programmer mode. Thanks 'PCM programmer'

Wish me good luck

[Edward]

Tried it this morning and it still doesnt work.
However, when I try to do an init 2 times, like below

main(){
lcd_init(); //Initialise LCD
delay_ms(10);
lcd_init(); //Initialise LCD
delay_ms(10);
}

Everything is okay. It puzzles me and hope anyone can answer why.
Anyway, I am now glad. Thanks and I really like the forum.

Best Regards,
Edward

[Ttelmah]