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AD75019

Discussion in 'Electronic Design' started by Mauricio, Jan 24, 2005.

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  1. Mauricio

    Mauricio Guest

    I´m trying to drive an AD75019 (16x16 Crosspoint Switch) with a PIC
    Microcontroller) I have seen the SIN and SCLK waveforms with a scope
    and everything seems to be right. But I can´t open or close any
    switch. Has somebody some PIC working code in order to see what I´m
    doing wrong?

    Thanks in advance.
     
  2. Andrew Holme

    Andrew Holme Guest

    Are you shifting data in too fast or too slow? SCLK must be between 20 KHz
    and 5 MHz.

    Are you pulsing the PCLK parallel load after shifting the data in?
     
  3. I've done this - it was a few years ago and I no longer have access to
    the PIC code. As I recall there's nothing particularly difficult *but*
    the input shift register is dynamic and has a minimum clock speed of
    (just looked it up) 20kHz. Once the switch configuration data is
    clocked in, it's latched and needs no further concern.

    Cheers
     
  4. Guest

    Hi andrew, thanks for reply.

    Yes, I´m Shifting data at 250 KHz, and after shift all the 256 bits
    I´m strobing the data with a low pulse at PCLK (width = 10uS)

    Mauricio.
     
  5. Andrew Holme

    Andrew Holme Guest

    How are you testing for switch closure?
    How are you biasing the analogue inputs?
    Are there any unused analogue pins? The datasheet doesn't say if
    unused inputs are allowed - you might try high value SIL resistors to
    GND.
    What power supplies are you using?
    Are you observing the correct setup and hold times (t1 & t3) as per the
    timing diagram on page 3 of the datasheet?

    If you change your software to shift more than 256 bits - you should
    see something coming out of SOUT - might be a useful test.
     
  6. Guest

    1.- I´m injecting a square wave at analogue input, and viewing the
    output with a scope.

    2.- from the square wave generator.

    3.- there are analog inputs unused but pulled down to ground

    4.- It´s a PC ATX 300 Watts power supply.

    5.- Setup timings seems to be right.

    6.- I did a test software that run my PIC in an endless loop Writing
    0x55 and SOUT is always High.
     
  7. Andrew Holme

    Andrew Holme Guest

    What voltage levels w.r.t. ground?
    Directly or through resistors? What value?
    That's not what I meant. What are the voltages on Vdd, Vss and Vcc
    relative to DGND.
    Something's wrong there.
     
  8. In message <>,
    writes

    Check that the clock is clocking continuously (at >20kHz) and manually
    connect the Sin pin to 0V and 5V alternately while looking at Sout. Sout
    should follow Sin (with a short delay). If it doesn't, you've probably
    got a duff chip. Make sure the power supply sequences correctly, or use
    Schottky diodes as suggested in the datasheet.

    Cheers
     
  9. john jardine

    john jardine Guest

    This is a straight copy of a setup routine for a block of 8 of these chips
    but shows that sending for say one chip, 80 bits of serial data, 80
    clocks, and the final update strobe is perfectly straightforward.

    regards
    john

    ;---------------------------------------------------------------------------
    ---------------
    DISABLE.THE.MATRIX.CHIPS
    ;shuts down all the outputs. Stops
    'multi-output' self destruct
    ;sends out 640 '0's (0=disable out/pin.
    1=enable it)
    ;this is a hardware routine only
    ldw 80 ;640 bits worth of zeroes in one lump
    wto scrap

    local1 ldw 8 ;bit count each byte
    wto scrap1

    local2 matrixdata.low ;force zeroes into chips
    matrixclock.high
    matrixclock.low
    decfsz scrap1,self
    goto local2
    decfsz scrap,self
    goto local1

    matrixupdate.low ;latch the data in to the 8 matrix chips
    matrixupdate.high
    RETURN ;having pumped 640 0's pumped out
    ;---------------------------------------------------------------------------
    -----------------
     
  10. Guest

    Thanks John.

    This is a pretty nice code, but there are some things I don´t
    undestand. Why must I load 640 zeroes into the shift registers if the
    Crosspoint only have 256 switches? I can suppose you´re initializating
    8 AD75019 connected in cascade, then my question is why only 80 bits
    per IC? Please comment.
     
  11. john jardine

    john jardine Guest

    Thanks John.

    This is a pretty nice code, but there are some things I don´t
    undestand. Why must I load 640 zeroes into the shift registers if the
    Crosspoint only have 256 switches? I can suppose you´re initializating
    8 AD75019 connected in cascade, then my question is why only 80 bits
    per IC? Please comment.

    Mauricio, my apologies. Ignore my post. The code is for a AD8113 chip, which
    is a 16X16 Video switcher.
    [Having just said that I've looked at the AD75019 data sheet and noticed the
    256 bits of data are serially loaded and latched the same way as the
    AD8113].
    regards
    john
     
  12. malvarezdel

    malvarezdel Guest

    Hi Andrew.

    Square wave is 0 - 5V (5Vpp)

    Vdd = +12V
    Vss = -12V
    Vcc = +5V

    Pull down resistors 100K from each input to ground
    Yes, something´s wrong here.

    Regards
     
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