lcd problems

[newguy]

Hi all,

Long time reader, first time poster.

I've done quite a bit of programming with CCS and pics (18f452, 252, 242, 16f877). However, I've run into a problem and I can't figure it out.

My present project uses an 18f242 and a standard 2x16 lcd character display. This is the first time that I've wired an lcd to port A, and I'm really beginning to question why I did that in the first place. Hindsight is always 20/20, I guess.

The code that I use to communicate with the lcd is basically the same code (lcd.c) that came with the ccs compiler. I've wired the lcd's D4-D7 lines to A0-A3, enable to A4, and rs to A5. Since A4 is an open drain output, I also have a pullup on that line. The lcd's R/W line is grounded, and I'm communicating with it in 4 bit mode. The relevant declarations follow:

struct lcd_pin_map {
int data : 4;
boolean enable;
boolean rs;
} lcd;

#byte lcd = 0xf80

void lcd_send_nibble( byte n ) {
lcd.data = n;
delay_cycles(1);
lcd.enable = 1;
delay_us(2);
lcd.enable = 0;
}

void lcd_send_byte( byte address, byte n ) {

lcd.rs = 0;
delay_us(350);
lcd.rs = address;
delay_cycles(1);
delay_cycles(1);
lcd.enable = 0;
lcd_send_nibble(n >> 4);
lcd_send_nibble(n & 0xf);
}

What gets me is this same code works when I connect an lcd to port C on a 18f252. The only change I make is the #byte lcd = 0xf82 to point to port C's memory location.

Everything else seems to work, since I can get the pic to toggle lines which control relays, and they click away just fine if I make them toggle. The lcd seems sort of like it hasn't been initialized properly, which means that the code above isn't doing what it's supposed to be doing.

And yes, analogs have been turned off. Can someone please tell me what I'm overlooking? Was hooking an lcd to port A a really stupid idea?



-- Mark

[Ttelmah]

[newguy]

[guote="TTelma"]Have you tried 'toggling relays' on portA?. If not, then the problem is almost certainly the initialisation of the port. On the 18F family, portA, also handles the analog inputs. By default it is configures in this way. Hence you have to add the line:
setup_adc_ports(NO_ANALOGS);

If you want to use the port for normal I/O.
There is nothing 'wrong' with using portA for the LCD. :-)

Best Wishes
[/quote]

Yep, did that. The port initializes properly, and timer0 is setup so that it uses the internal source, not the external source on pin A4.

Here's the initialization code:

[Guest]

Your problem might be that your enable pin (RA4) has a pullup which pulls the signal H during program reset thus causing one pulse on E which the display might misinterpret ...

Just try to swap your E and RS pins as a pulse on the RS line should not cause any harm and check if the problem is still there.

hope this helps

[Guest]

Are you reseting the WDT? TTY

[newguy]

[curt2go]

[Guest]

[rnielsen]

You might want to be careful about simply connecting your R/W line to ground. I've done several projects using 1 and 2 line displays with the R/W line tied to ground. It works fine but every once-in-a-while I would get garbage on the display and would need to cycle power to get it to go away. After digging into the actual requirements I found out that it is best if you check the 'busy' flag each time you want to send a command or data to the display. Here's the code that I came up with. It might not be the cleanest code but since I have started using it I have not had any problems with any of my LCD displays 'wigging' out.

I have the display lines connected up in the following order:

MCU---------LCD
PIN_A0-----DB4
PIN_A1-----DB5
PIN_A2-----DB6
PIN_A3-----DB7
PIN_A4-----ENABLE
PIN_A5-----RS
PIN_E0-----R/W

This code is for a 1X16 display. Modify it slightly to be used for a 2X16.

//////////////////////
#define ENB PIN_A4 // enable for the LCD display
#define RS PIN_A5 // RS pin of the LCD display
#define RW PIN_E0 // R/W bit for the LCD display

void pulse(unsigned int8 bits) // sends out the clock pulse to the LCD display
{
output_high(ENB);
output_a(bits);
delay_cycles(2);
output_low(ENB);
}

void bf_check(void) // checks the 'busy flag' for the LCD chipset
{
int1 BF = 0;

set_tris_a(0x0F);// set bits 0-3 as inputs
output_low(RS);
output_high(RW);
delay_cycles(3);

do
{
output_high(ENB);
delay_cycles(6);
if(input(PIN_A3))
{
BF = 1;
}
else
{
BF = 0;
}

output_low(ENB);
delay_cycles(3);
output_high(ENB);
delay_cycles(6);
output_low(ENB);

}while(BF);

set_tris_a(0x00);// set all bits to outputs
}

void ctlnib(int8 niblet) // sends a control command to the LCD display
{
int8 msn, lsn;

bf_check();

msn = niblet & 0xF0;
msn = msn >> 4;
msn = msn | 0x10;

output_low(RW);
output_low(RS);

pulse(msn);
lsn = niblet & 0x0F;
lsn = lsn | 0x10;
pulse(lsn);
}

void datnib(int8 niblet) // sends a data byte to the LCD display
{
int8 msn, lsn;

bf_check();

msn = niblet & 0xF0;
msn = msn >> 4;
msn = msn | 0x30;

output_low(RW);
output_high(RS);

pulse(msn);
lsn = niblet & 0x0F;
lsn = lsn | 0x30;
pulse(lsn);
}

void disline(char outstr[], int8 dline) // format is; string - line
{ // displays a line of text on the LCD display
int8 llg, dindex, track;

track = dline;
ctlnib(dline);
llg = strlen(outstr);
for(dindex = 0; dindex <= llg - 1; dindex++)
{
if(track == 0x88) //this is for 1X16 displays, modify this section for 2X16 displays
{
ctlnib(0xC0);
}
datnib(outstr[dindex]);
track++;
}
}

void initdisp(void) // initialize the LCD display
{
output_low(RW);
delay_ms(30);
pulse(0x03);
delay_ms(10);
pulse(0x03);
delay_us(300);
pulse(0x03);
pulse(0x02);
ctlnib(0x28);
ctlnib(0x80);
ctlnib(0x01);
ctlnib(0x06);
ctlnib(0x0C);
}

Hope this might help. :o)

Ronald