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Question about interface between DAC8782 and TMS320C28346

Byoungkil Jung
Prodigy 160 points

Other Parts Discussed in Thread: DAC8728, TMS320C28346, SN74HC138

Hello,

I'm designing a board based on the TMS320C28346 and DAC8728.
And I have a question about timing diagram(Figure 4. Wirte Operation 2 on page 12).

At the XINTF timing of C28346, /CS is longer than R/W signal.
But, at the timing of DAC8782, /CS is shorter than R/W signal.


in our system,/CS timing is 46.66nsec.
(Lead : 6.66nsec, Active : 33.33nsec, Trail : 6.66nsec)

Is it possible interfacing between C28346 and DAC8728?
Answer please.
Thank you.

  • 0
    TI__Guru**** 182901 points
    Hi Byoungkil,

    With /CS longer than R/W on the DAC8728, you may have issues getting the expected data into the DAC registers. You should look into using something like an SN74HC138 address decoder to act as the /CS input to your DAC8728. There is a document describing the XINTF of the TMS320C28346 here: www.ti.com/.../sprufn4a.pdf that you may want to review. You can adjust the lead and trail times of the address bus around the active time of the R/W strobe.
  • 0 in reply to Tom Hendrick
    Prodigy 160 points

    Hi Tom,

    As your opinion, I should use something circuit for the /CS of DAC8728, right?

    I think additional circuit as below:(/WE, /RD, R/W are signal from C28346)

    As above figure, falling edge scheme is satisfacted, but rising edge scheme is not satisfacted.

    Can you recommend something nice circuit?

    Best Regards.

  • 0 in reply to Byoungkil Jung
    TI__Guru**** 182901 points

    Hi Byounfkil,

    Using combination logic with the /WE and /WR strobes can be problematic since there are probably other devices on the shared memory bus - like memory for example.  If there is nothing else on the XINTF, you might be able to do this and use a DFF to clock/latch the /CS.  The address decoder I suggested allows you to put the DAC8728 at a 'known address' on the databus and then you can simply write to or read from that specific address.