Printing Integer Value to LCD in ASCII Format

[JTerry]

Hey again,

I've had a lot of help from the board in sorting out a Pedometer circuit I'm currently working on as part of a group project.

Unfortunately, we've been using the sprintf function to write the value of an integer 'noofsteps' into a character string, which was then written to the screen. Now that we've come to try and compile the completed code, it's too long to fit onto the chip (PIC16F684).

As suggested by members of this forum, I've looked at trying to accomplish what I'm trying to do without using sprintf (as I don't need anywhere near all of the functionality that sprintf allows).

Currently I'm trying to do the follow:

I have an integer called 'noofsteps', which will have a value between 0 and 20,000. I want to take the value of 'noofsteps' and display it on my LCD screen (Hitachi 44780) without using sprintf as it's too memory intensive.

I'm currently trying to implement this snippet I found elsewhere:

value = 12345;	// number you want to display
length = 5;              // five digits	
div = 10000;	// divisor


while( length )
{
 lcd_write( (value / div) + 48 );	// write highest digit first
 value = value % div;
 length--;
 div /= 10;
}

But as a complete beginner, I'm having trouble getting my head around how this could be integrated into the rest of the program.

I understand how this strips the integer number apart into its component numbers and then adds 48 so that each decimal number aligns to its ASCII equivalent.

However, what I don't understand is how I would write each number to my screen in sequence without removing the digit that was there before it. I.e. in this case, how to output "1", then shift the cursor on the screen to the right, then output "2", then shift the cursor to the right... etc. I'm guessing this information would be in the Hitachi 44780 Datasheet but I've got no clue how to find it, or even really what I'm looking for. For information, I am using the Hitachi 44780 in 4 BIT OPERATION.

Secondly, I'm confused as to what

while(length)

does? Does it simply loop the code below until 'length' = 0?

Would anybody be able to offer some pointers? Unfortunately I'm away from the programming equipment until 4th Jan so I won't be able to test anything until this, but it would be good to know that I am moving along the right lines.

Thanks in advance for any help that people may be able to give, and please remember that I am a total beginner and will be asking stupid questions in response to your answers!

Thanks,

JT

[tabstop]

Hey again,

I've had a lot of help from the board in sorting out a Pedometer circuit I'm currently working on as part of a group project.

Unfortunately, we've been using the sprintf function to write the value of an integer 'noofsteps' into a character string, which was then written to the screen. Now that we've come to try and compile the completed code, it's too long to fit onto the chip (PIC16F684).

As suggested by members of this forum, I've looked at trying to accomplish what I'm trying to do without using sprintf (as I don't need anywhere near all of the functionality that sprintf allows).

Currently I'm trying to do the follow:

I have an integer called 'noofsteps', which will have a value between 0 and 20,000. I want to take the value of 'noofsteps' and display it on my LCD screen (Hitachi 44780) without using sprintf as it's too memory intensive.

I'm currently trying to implement this snippet I found elsewhere:

value = 12345;	// number you want to display
length = 5;              // five digits	
div = 10000;	// divisor


while( length )
{
 lcd_write( (value / div) + 48 );	// write highest digit first
 value = value % div;
 length--;
 div /= 10;
}

But as a complete beginner, I'm having trouble getting my head around how this could be integrated into the rest of the program.

I understand how this strips the integer number apart into its component numbers and then adds 48 so that each decimal number aligns to its ASCII equivalent.

However, what I don't understand is how I would write each number to my screen in sequence without removing the digit that was there before it. I.e. in this case, how to output "1", then shift the cursor on the screen to the right, then output "2", then shift the cursor to the right... etc. I'm guessing this information would be in the Hitachi 44780 Datasheet but I've got no clue how to find it, or even really what I'm looking for. For information, I am using the Hitachi 44780 in 4 BIT OPERATION.

I've not used LCDs much, but isn't that sort of The Complete Opposite to how they usually work? (I've searched Hitachi 44780 enough to verify it's dot matrix and not seven-segment.) Once you've got them into accepting data mode, I seem to remember you just start sending bytes down the pipe and they show up. That is to say, you doing "send (12345)" is you sending five bytes to the LCD, and you doing "send(1) send(2) send(3) send(4) send(5)" is you sending five bytes to the LCD. The LCD has no way of knowing, and doesn't care, which one it is, right?

Secondly, I'm confused as to what

while(length)

does? Does it simply loop the code below until 'length' = 0?

That's what while does. It loops until the thing in the parentheses is false (false means zero).

[anduril462]

I suggest going back and looking though your previous post.

As suggested by members of this forum, I've looked at trying to accomplish what I'm trying to do without using sprintf (as I don't need anywhere near all of the functionality that sprintf allows).

Currently I'm trying to do the follow:

I have an integer called 'noofsteps', which will have a value between 0 and 20,000. I want to take the value of 'noofsteps' and display it on my LCD screen (Hitachi 44780) without using sprintf as it's too memory intensive.

I'm currently trying to implement this snippet I found elsewhere:

value = 12345;	// number you want to display
length = 5;              // five digits	
div = 10000;	// divisor


while( length )
{
 lcd_write( (value / div) + 48 );	// write highest digit first
 value = value % div;
 length--;
 div /= 10;
}

But as a complete beginner, I'm having trouble getting my head around how this could be integrated into the rest of the program.

I understand how this strips the integer number apart into its component numbers and then adds 48 so that each decimal number aligns to its ASCII equivalent.

Salem wisely suggests using itoa if it's available. If not:
Based on your last post's code, I would put the chars directly in TopMessage or BotMessage instead of calling lcd_write on each one. I also would do my loop like so:

void num_to_str(int num, char *str)
{
    int div = 10000; // this is big enough for 20000 steps
    int flag = 0;  // track if we've started printing yet -- this is for "trapped" zeros like 2001
    int i = 0;
    char c;
    while (div) {
        if (flag || num > div) {
            c = num / div + '0';
            flag = 1;
        }
        else {
            c = ' ';  // put a space char since we haven't started printing the number yet
        }
        str[i++] = c;
        num %= div;    // get rid of the first digit
        div /= 10;   // shrink the divisor
    }
}
...
num_to_str(12345, &TopMessage[6]);  // puts "12345" into TopMessage starting at the 7th character

However, what I don't understand is how I would write each number to my screen in sequence without removing the digit that was there before it. I.e. in this case, how to output "1", then shift the cursor on the screen to the right, then output "2", then shift the cursor to the right... etc.

Not a problem. You wrote the following instruction in the code from your previous post:

    LCDWrite(0b00000110, 0);    //  Move Cursor After Each Character

So just put the number directly into TopMessage or BotMessage, then call LCDOutput().

[stahta01]

Did you try the non standard itoa from <stdlib.h>

It exists in Hi-Tech C

extern char * itoa(char * buf, int val, int base);

Tim S.

[JTerry]

Hey guys, thanks again for the help.

Is itoa much smaller than sprintf? That seemed to be the largest part of the previous code that was written, and the reason that we were filling the chip memory.

If not, I will look to try your code Anduril, but unfortunately I'm away from the kit at the moment due to various holidays etc.

Thanks a bunch for everyone taking to time to post a response, this is a great resource and I appreciate the patient help.

JT

[anduril462]

Yes, itoa is much smaller. It's probably a few dozen lines at the most, where as sprintf will run into the hundreds since it has to handle so many different types of data (ints, floats, chars) and the numbers can have a wide variety of formats. The code I gave you is basically itoa, so if Hi-Tech C has it, as stahta01 states, use it.