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Driving a DS1393 from a PIC or AVR

Discussion in 'Electronic Basics' started by Mike Deblis, Dec 8, 2004.

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  1. Mike Deblis

    Mike Deblis Guest


    Has anyone tried talking to a DS1393 or similar 3-wire RTC from either
    a PIC or AVR (or similar) - these RTCs are not SPI - they have a
    bi-directional I/O pin.


  2. Isn't it really just I2C protocol with a chip select as the "third"
  3. I'd be very 'wary' about chosing this chip, since it is no longer listed
    by Dallas/Maxim, with the data sheet 'links', going to a blank page...

    Best Wishes
  4. Hmm.... I just went to and typed in ds1393 in the part
    number search field, clicked the "PART NO. SEARCH" button and came up
    with this page:

    The datasheet link worked fine for me as well. It's one datasheet for
    the DS1390, DS1391, DS1392, and DS1393. Where did you look?
  5. Jeroen

    Jeroen Guest

    I'm using a DS1302 for a project which also has only 3 wires. It's really
    simple and just like SPI, except that it's half duplex.

    You can easily bit bang it. Switch the data in/output to output, make /CS
    low, output 8 databits+clocks, then change the in/output to input, and issue
    the neccessary clocks and sample the input. 20-25 lines of C code.

    something like:

    (assuming AVR, port B... 0=cs 1=dat 2=clk)

    #define CS 1
    #define DAT 2
    #define CLK 4
    DDRB|=DAT; // switch the data line to output
    PORTB&=~CS; // select the chip
    for (i=0;i<8;i++) // output 8 bits of command
    if (command & 128) PORTB|=DAT;
    else PORTB&=~DAT;

    PORTB|=CLK; // Toggle clk. DS sample the data bit
    command<<=1; // Shift command, maybe insert some NOPs here to delay
    if it goes too fast
    if (i!=7) PORTB&=~CLK; // Don't set CLK low at the last bit to prevent
    shorting two outputs together

    DDRB&=~DAT; // Switch to input
    PORTB&=~CLK; // Set CLK low, DS13XX switches to output, takes at max 160ns

    for (i=0;i<8;i++) // Fetch 8 bits
    if (PORTB & DAT) data|=1;


    PORTB&=~CS; // End transfer

    I've successfully interfaced many chips this way and for an RTC, speed is
    not really an issue. Just follow the timing diagrams in the datasheet.

    Actually, Dallas has an appnote of this, app note 2361...

    Hope this helps,

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