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DAC7552: Input register description.

Peter Morrow
Prodigy 50 points
Part Number: DAC7552

Hello,

I'm trying to program a DAC7552, but there doesn't seem to be much information on the roleof the input register on this DAC in the datasheet.  Would it be possible to explain to me the role of the this register?

It is mentioned in the serial programming interface section and the block diagram, however I don't think there is any explanation as to how the value in this register affects the output voltage.

The DAC register is documentated and looks like the value of the DAC register affects the voltage output (in the D/A section), however it isn't clear to be how the input register features.

At this point I'm unsure if I need to write to the input register, DAC register or both in order to vary the output voltage of this DAC.


Many Thanks,
Peter Morrow.

  • 0
    TI__Guru 52683 points

    Hello Peter,

    The DAC7552 describes this functionality in the section titled "16-Bit Word and Input Shift Register".  The 16-bit word consists of 4 control bit (shown in Table 1) and 12 bits of DAC data.  The data format is straight binary, so 0x000 represents a 0V output, while 0xFFF represents a Vref - 1LSB output.  The 4 control bits set the channel, update mode, and other features.  This 16 bit word register is the only register in the device.

    Please let me know if that answers your question, or if you have any more questions.

    Thanks!

    Paul

  • 0 in reply to Paul_Frost
    Prodigy 50 points

    Hi Paul,

    Thanks for your response!  So it seems to affect the voltage output from the DAC I need to set the control bits to update the input register AND the DAC register?  Setting the control bit to update the input register would not be enough?

    I'm referring to the section "Table 1. Serial Interface Programming" here.

    From this it looks like writing to the input register just stores the value in the device but does not have any affect on the output voltage.

    I am guessing someone might write update just the input register if they want to store the value but then output the requested voltage later?  A sequence for this would look like:

    Write to device (ctrl bits: only update input register).

    Write to device with new value ((ctrl bits: both input and dac) moves old input register contents to the DAC register and updates input register with new value)?

    If you wanted to immediately change the voltage output by the DAC it would be:

    Write to device (ctrl bits: update input and DAC register).

    Could you check my understanding here please? Many thanks for your help.

    Peter.

  • 0 in reply to Peter Morrow
    TI__Guru 52683 points
    Hi Peter,

    The multiple update scenarios are in place to allow the user to update both channels synchronously or asynchronously. If you desired to write to to a single channel and have the DAC output assume the new value at the same time you would use the 'Single Channel Update' for the desired channel. For example, if you wanted to set DAC A to mid-scale (0x800) and update the channel immediately, you would use the control bits b'0100 or 0x4. The full 16 bit word would be 0x4800.

    Let me know if you have any more questions,
    Thanks!
    Paul
  • 0 in reply to Paul_Frost
    Prodigy 50 points
    Thanks Paul for your help.

    Peter.