PIC Tutorial - I2C Clock Board
I2C Clock Board
This is the I2C Clock Board, it uses a PCF8583P, which is a real time, battery backed, CMOS I2C clock chip in an 8 pin DIL package. The actual chip I'm using here (as shown in the picture) is labelled 'Intersil 7313', and came from a Grundig VS920 video recorder, but it's pin compatible with the original Philips chip (which is what's actually listed on the circuit). Notice that this chip only has one address line, so can only be mapped as either page 0, or page 1.
The circuit is very similar to the previous I2C EEPROM board, with a few additions, a 32KHz clock crystal and trimmer (using two of the previous address lines), an extra alarm output complete with 12K pull-up resistor (connected to RB4), and components for the battery backup circuit (D1 and D2 are isolating diodes). When the board is powered up the chip is supplied with 5V through D1 (which drops 0.7V leaving 4.3V on the chip), D2 is reverse biased and passes no current. When the board isn't powered, D2 passes current from the battery (only around 2uA, giving a long battery life) to the chip, and D1 is reverse biased, isolated the rest of the circuit. The 3V battery shown is a lithium disk type, and usually lasts around 5 years in the Grundig VCR's that use this same chip. The trimmer is for setting the accuracy of the clock, and if accurately adjusted should keep good time.
Although it's labelled as connecting to PortB, as with most of the boards, it can also be connected to PortA if required.