OK. Let's see what we can do.
First of all, you haven't mentioned what sort of display you want to use to display the time. Second, since it's a school project, I'll just give you some tips you can use to build your own solution rather than posting finished code.
Your first task is to become familiar with the internals of the DS1307. You can find the data sheet here: <A href='http://datasheets.maxim-ic.com/en/ds/DS1307.pdf' Target=_Blank>External Web Link</a> If you haven't previously done so, please download and familarize yourself with this document before proceeding.
The data format used by the 1307 is, for the most part, BCD, with the most significant decimal digit stored in the top four bits, and the least signifgant decimal digit stored in the bottom four bits. PicBASIC has a function, bcdtoascii, that you can use to easily parse these two packed BCD digits into ASCII characters that you can send to a display.
Handling the Hours register is a little tricky. Contained in the upper bits of that register is a flag (bit 6) that sets the 1307's internal timekeeping format to either 12 or 24 hour mode. When you set the time, you need to either set or clear this bit, depending upon your desired timekeeping format. Also, in 12 hour mode, a flag in bit 5 indicates either AM (cleared) or PM (set).
Let's say you're going to use 12 hour mode, and the time is 3 AM. You're using b6 to store the value that you'll be writing to the 1307's Hours register. You'd set the time like this:
1. First, load the time into b6:
<code><pre><font size=2 face='Courier'>
b6 = $03
</font></pre></code>
2. Set the 12/24 hour flag:
<code><pre><font size=2 face='Courier'>
b6 = b6 | %01000000
</font></pre></code>
3. It's AM, so clear the AM/PM flag:
<code><pre><font size=2 face='Courier'>
b6 = b6 & %11011111
</font></pre></code>
Now b6 is ready to be written to the 1307 when you set the time.
Likewise, when you read the Hours register, you need to first, capture and store the AM/PM flag's state, then strip the AM/PM flag and 12/24 hour flag bits before you process the Hours register value in your display routine.
Let's say that you're using b9 to temporarily store the state of the AM/PM flag, and that you've read the 1307's raw Hours register value into b6. You can also use b9 as a scratchpad register, as shown below:
<code><pre><font size=2 face='Courier'>
b9 = b6 & %00100000 'capture the AM/PM flag's value
if b9 > 0 then 'save the flag's value
b9 = 1
else
b9 = 0
endif
b6 = b6 & %00011111 'strip flag bits
bcdtoascii b6,b0,b1 'ASCII hours x 10 value to b0, hours x 1 value to b1
</font></pre></code>
Processing the rest of the 1307's registers is straightforward.
When I initialize a 1307, I first wait one second after the program starts, then make
sure the CH bit (bit 7 of the Seconds register) is cleared. Also, since the 1307 is probably running on a backup battery when I start my program, I make sure that I don't
change the 1307's time value while I'm initializing the chip. Here's how I do that with the seconds register, and initialize the chip to the 12 hour format while I'm at it:
<code><pre><font size=2 face='Courier'>
Main:
pause 1000
i2cslave %11010000,i2cslow,i2cbyte
pause 100
readi2c 0,(b0) 'clear the CH bit
b0 = b0 & %01111111
writei2c 0,(b0)
readi2c 2,(b0) 'set 12-hour display format
b0 = b0 | %01000000
writei2c 2,(b0)
.
.
.
end
</font></pre></code>
Finally...
You'll probably want to have your program read the time in a loop. It doesn't make any sense to update your time display each time your loop reads the 1307's time, so you'll probably want to update your display only when the seconds change.
To do this, set a variable to store the value of the previous seconds value:
<code><pre><font size=2 face='Courier'>
symbol PrevSecs = b13
</font></pre></code>
In your loop, read the seconds value like this, then call your display routine only when needed:
<code><pre><font size=2 face='Courier'>
do
readi2c 0,(b0)
if b0 <> PrevSecs then
PrevSecs = b0
gosub DisplayTime
endif
loop
</font></pre></code>
That should be enough to get you started. If you have further problems as you work through your assignment, feel free to post them here.
Have fun!
Tom
Edited by - Tom2000 on 23/08/2007 11:03:19
Edited by - Tom2000 on 23/08/2007 11:05:20
Edited by - Tom2000 on 23/08/2007 11:14:49
