Electronic – What are similarities between RTC DS1374 and RTC DS1307

You probably have the target chip address wrong. You are sending 68h. Either that is not the address of the chip or it is not wired right. The two sequences you show are first a write then a read to that address. In both cases, no ACK was received so the sequence was terminated. Check the datasheet for the chip address.

Added:

I just looked in the datasheet, and the address of that chip really is 68h (page 12), so that's not the issue. That leaves something not wired right at the chip. Your scope traces look good in that a correctly wired and working chip should have responded with ACK as far as I can tell.

So thanks to the help of all here here's an alternative solution using the RTCC of the pic.

This solution makes much more sense then reading the time from an external SPI module.

you can buy a 32.768 crystal like this one: http://www.sparkfun.com/products/540

and two 11pf or 12 pf crystals and align them as shown on this schematic (top right): http://www.sparkfun.com/datasheets/DevTools/PIC/UBW32_MX795_v262.pdf

What I've still not figured out is how to power the RTC with an additional battery. If someone knows how I'd enjoy a post!

Here's a working example code:

// Master header file for all peripheral library includes
#include <plib.h>

// configuration settings
#pragma config FNOSC = PRIPLL, POSCMOD = HS, FPLLMUL = MUL_18, FPLLIDIV = DIV_2, FPBDIV = DIV_2, FPLLODIV = DIV_1
#pragma config FWDTEN = OFF

int main(void) {

    rtccTime    tm;          // time structure
    rtccDate    dt;          // date structure

    // Configure the device for maximum performance.
    // This macro sets flash wait states, PBCLK divider and DRM wait states based on the specified
    // clock frequency. It also turns on the cache mode if avaialble.
    // Based on the current frequency, the PBCLK divider will be set at 1:2. This knoweldge
    // is required to correctly set UART baud rate, timer reload value and other time sensitive
    // setting.
    SYSTEMConfigPerformance(72000000L);

    RtccInit();   // init the RTCC

    while(RtccGetClkStat()!=RTCC_CLK_ON);   // wait for the SOSC to be actually running and RTCC to have its clock source
                                            // could wait here at most 32ms

    RtccOpen(0x10073000, 0x07011602, 0);    // set time and date (- actually i don't know what time is set, but for the moment it doesn't matter.)
                                            // time is MSb: hour, min, sec, rsvd. date is MSb: year, mon, mday, wday.
                                            // please note that the rsvd field has to be 0 in the time field!

    RtccGetTimeDate(&tm, &dt);              // get current time

    DDPCONbits.JTAGEN = 0; // disable JTAGport, free up PORTA
    TRISA = 0b0000000000000000;
    TRISB = 0b0000000000000000;

    while(1){

        RtccGetTimeDate(&tm, &dt);

        // test: minutes odd or even
        int minutes = tm.sec%2;
        switch(minutes){
            case 0:
                PORTA = 0b0000000000000000;
                PORTB = 0b1111111111111111;
                break;
            case 1:
                PORTA = 0b1111111111111111;
                PORTB = 0b0000000000000000;
                PORTA._RA0 = 0;

                break;
        }
    }
}