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DAC8541 - Can the I/O pins ever be Hi-Z and when will that be?

Walter Wise
Prodigy 40 points
Other Parts Discussed in Thread: DAC8541

DAC8541 http://www.mouser.com/ds/2/405/slas353-117934.pdf is DAC8541 I need to know if CS being high always or never means data inputs (DB0-DB15)are Hi-Z, (tristate, 'disconnected') and/or, if using Note 4 above Figure 1 timing diagram, (CS and WR always low) means inputs (DB0-DB15) are Hi-Z all the while LDAC is High (assuming not during rising to input new data), or if they are Hi-Z while LDAC is Low, or ever at all. My need is to have a time when I/O is Hi-Z from Bus, and if either or both of the above ideas can achieve that, or some other idea (other than another buffer or driver chip) I will be grateful for an explanation or some guidance. I'd appreciate a couple samples, also, to experiment with, but now this is on E2E so where do I even ask? New to here. This is for a new proposed design to upgrade an existing prototype. Thank you.

  • 0
    TI__Genius 10615 points

    Hi Walter,

    Walter Wise said:
    I need to know if CS being high always or never means data inputs (DB0-DB15)are Hi-Z, (tristate, 'disconnected')

    They will always be Hi-Z unless R/W is HIGH, so either of your ideas will work.

    Walter Wise said:
    I'd appreciate a couple samples, also, to experiment with, but now this is on E2E so where do I even ask?

    You can do this by clicking here and clicking on "Request Sample". You can follow the instructions from there.

    Let me know if you run into any problems.

  • 0 in reply to Eugenio Mejia
    Prodigy 40 points

    Thank you. Really, I meant totally Hi-Z from the bus, and during a write, though DAC8541 asserts no data to the bus, it apparently can still "see" the bus or it could not perform its write function. Now I realize that if I don't want the data that is on the bus at a certain time, I only need to avoid asserting LDAC and the output will not update. If ever I need it to really be Hi-Z and oblivious to the bus altogether, I guess I need to set CS high . . . Does that make sense? Thanks for your answer. BTW, I guess there are no samples available, and was not able to buy them, either, as maybe they have to be ordered in sets of 1K or ?...

  • 0 in reply to Walter Wise
    TI__Genius 10615 points

    Walter Wise said:
    If ever I need it to really be Hi-Z and oblivious to the bus altogether, I guess I need to set CS high

    Yes, this would be the best approach. Otherwise the input resistance will be about ~700kΩ.

    Walter Wise said:
    BTW, I guess there are no samples available, and was not able to buy them, either, as maybe they have to be ordered in sets of 1K or ?...

    No, you don't need to order a 1k units. You should be able to order a couple of devices from the samples program. Did the link that I give you give you problems? I was able to go through the whole process of ordering without any issues.

  • 0 in reply to Eugenio Mejia
    Prodigy 40 points
    OK I see what happened. I "don't have access to samples" since maybe I am not a recognized business. Not in school, either. So with shipping 2 are about $22. I'll have to think that over, but at least my technical questions seem to have been answered/verified. Thanks again.