DS1307 Question

crukid88 · Joined: 04 Oct 2007 Posts: 14

referring to the data sheet,if I am not wrong it says that the data that will be retrieved is binary coded decimals so e.g 10 in binary is 00010000. I hope I am correct. How do we write and assign values in the RTC register?should it normally be decimals or we will format it to BCD?

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

See this DS1307 driver in the CCS Code Library.
http://www.ccsinfo.com/forum/viewtopic.php?p=46052
Note that it uses bin2bcd() and bcd2bin() conversions when writing or
reading from the DS1307 date/time registers.

Douglas Kennedy · Joined: 07 Sep 2003 Posts: 755 Location: Florida

Ten in bcd is encoded as 00010000 in an 8 bit storage location eleven would be 00010001. That means the high nibble which in pure binary represents sixteen times the numerical weight of the low nibble now only represents ten times the weight in bcd. A routine like the following takes advantage of the fact that ten is eight plus two and eight and two divisions are equivalent to shifting.