Set time / date on DS1307

[Ed Arnold]

I am using stuctures on a DS1307 RTC. I want to use 3 push-buttons to set the time and date on this RTC. 1 button for increment, 1 button for decrement, and 1 for enter/next value. The time structure looks like this:

struct time
{
int hr;
int min;
int sec;
}t, *p_t;

I have all of the read, write and control fuctions for the RTC. What I need is a better understanding of pointers and stuctures. I can better explain what I want with my non-working code fuction. I hope someone can show me how to make this work. The code here is only for set time, but you can get the general idea, I hope.

set_time_date()
{
int i=0;
int const LIMIT[5] = {23,59,12,31,99}; //used to force limits
clock_read(&t,&d);
printf(lcd_putc,"\fSet Time");
lcd_goto_xy(15,1);
printf(lcd_putc,"\%x:\%x", t.hr, t.min);
while(i<2) //how many times enter/next value is pressed
{
switch(KPbuff[Kout]) //keypress routine found in rtcc
{
case 'E': //this is enter keypress
*p_t++; //increment to next element in structure
i++;
break;
case 'U':
*p_t=--(*p_t)\%LIMIT[i]; //this won't compile but I want
//it to decrement what p_t points to.
lcd_goto_xy(15,1);
printf(lcd_putc,"\%x:\%x", t.hr, t.min);
break;
case 'D':
*p_t=++(*p_t)\%LIMIT[i];
lcd_goto_xy(15,1);
printf(lcd_putc,"\%x:\%x", t.hr, t.min);
break;
default:
break;
}
}
I realize this code may not be possible, but I am sure there is a simple way to do it. I want to keep this function simple. I don't want to use up alot of RAM or program ROM to accomplish this. Again thanks to the group for any help on this.
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This message was ported from CCS's old forum
Original Post ID: 1532

[Tomi]

First of all, there is a problem about the increment/decrement usage of your code. I think you want to select the next struct element with this: *p_t++; But it is illegal because the (*p_t) is not an integer type (e.g. char, int, int16, etc.). (*p_t) is a structure. (Note: in your original concept you must declare an independent char* pointer (e.g. myptr), use the "myptr = (char *)p_t" at start and then use myptr++ to access the next element in the struct. p_t++ means the next struct in an array and not the next element in the struct - the pointer is incremented by 3 in your example.)
Next, using the \% (modulo) operator is not a really good idea. It means a division (unless the second parameter for the \% is 2**N) but the division is always a pain using small microcontrollers like PICs. Use a simple compare what is a subtraction.
Next, I think you have choosen a difficult way. It would be better to use a simple char array.
Finally, "\%x" writes a value in hex. If your numbers are figured as binary (not BCD) use "\%02u". If your numbers are BCDs, you have a small problem with incr/decr.
All in all, here is a modified code: (note that I have changed the incr/decr operators; I think "U" is "up" and "d" is "down" ; sorry, I removed the lcd_putc from printf to test the code)
char t[3]; // instead of struct:t[0]=hour, etc.

printf(...... , "\%02u:\%02u", t[0], t[1]);

case 'E': //this is enter keypress
i++; // increment the index
if (i>2) i=0; // if index overflow: back to hours
break;

case 'U': // up???
t[i]++; // increment the appropr. array element
if (t[i] > LIMIT[i]) t[i] = 0; // instead of modulo
printf(..... , "\%02u:\%02u", t[0], t[1]);
break;
case 'D': // down???
if (t[i] > 0) t[i]--; // normal decr.
else t[i] = LIMIT[i]; // =0 before decr.: load it from LIMIT
printf(..... , "\%02u:\%02u", t[0], t[1]);
break;
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This message was ported from CCS's old forum
Original Post ID: 1539