sending ASCII characters

[axmanjr]

I have a very noob-ish question. How do you send ASCII characters? I am using a PIC chip and am interfacing it with a serial graphic LCD (DX160, from Sparkfun). The data/info sheet says to send ASCII[186], or whatever number, to do certain tasks such as clear screen and so on. For right now, I want to write a very simple code to test the LCD screen. I have the serial wire from the LCD plugged into PIN_B2 of the chip. I have:

#use rs232(baud=9600, parity=N, xmit=PIN_B2, rcv=PIN_B3, stream=LCD, bits=8)

at the top of my code and have tried to send data to it by using:

fputc(186,LCD);

Is this the best/proper way of doing this? Any help is appreciated.

[PCM programmer]

[axmanjr]

Hi, thanks for the response. Yes, PIN_B2 is connected directly to the DX160's TTL pin. Also, I'm using the PIC18F4680 and I think my compiler version is 3.23 (haven't checked in a while).

Is it possible to setup the fputc statement in a loop, to send multiple ASCII characters to the DX160, like this:

//***********
char buffer[10];
int m;
buffer[0] = 186;
buffer[1] = 194;

for(m=0; m<2; m++)
fputc(buffer[m], LCD);
//***********

I'll mess with this more when I get home tonight. I noticed the datasheet saying something about being cautious with your delay settings. I think I have mine way to low.

[PCM programmer]

Yes, you can do a loop that way.

Note that the DX160 data sheet says the baud rate is 57600, not 9600.

[axmanjr]

Thanks, I'll give that a try and update later!

[axmanjr]

Success! Thanks again for your help! It worked, after much debugging and "trial and error" routines... I ended up sticking with the default 57600 BAUD rate. I realized that I had to use PIN_C6 for TX (hardware UART) because the software UART apparently had a limited BAUD rate range. It couldn't reach 57600. And switching the BAUD rate to something else was a pain. The program would freak out... So I stuck with 57600.

After solving other issues, I got the screen to display random boxes and simple text.

Again thanks!

[axmanjr]

Question: If I want to use a 57600 BAUD rate to communicate to the LCD screen, would I need to use a specific crystal frequency to accomodate that?

Currently I am using a 4MHz crystal. But I am noticing a big lag when writing to the LCD screen, a big delay everytime something is being written to the screen.

[Ttelmah]

If it is working, then you are sending close enough to 57600bps. At 4MHz, you will actually be sending at 58823bps, which is the closest that the hardware can do from this clock. Just over 2% 'fast'. Normally anything up to about 3 to 4%, is considered 'acceptable' (RS232 has some margin here...).
It depends how much data is being sent, and how you are sending it. If (for instance), you are performing significant arithmetic, this will take time, and would be quicker on a faster chip.
However you may find the display itself 'buffers' the data, and only performs an update some time latter (not uncommon). Things lke a clear screen, can take quite a long time.
Simple output of ASCII characters as shown, will be as fast as 'possible, on just about any clock rate!. However it can be suprising what slows things down. For instance, a simple array access, may easily take 20 or more instructions. At 4Mhz, there is time for 173 instructions between each character. If you are doing something else (timer interrupt for example), time might well become short.
What is the chip?. The maximum clock rate depends on this.

Best Wishes

[Guest]

Thanks for the input. I'm not sure what the chip on the LCD is at the moment, but I am interfacing it with a PIC18F4680