• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 45 subscribers
  • Views 496 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS8685: What is latest conversion result?

Takuya
Prodigy 50 points
Part Number: ADS8685


Hi,

Three ADS8685-s is connected to FPGA(MAX10) with daisy-chain.
The FPGA communicates with the converters by SPI(not multi-SPI). The FPGA is SPI master.

According to the below: the datasheet(ads8685.pdf, revC) p44 section 7.5.3, the specification describes that the converter outputs the latest conversion result by NOP command.

Question 1: When sending a NOP in Frame F, Which is the "latest", the result of A or B?

Question 2: What is output in Frame F when READ command in Frame (F-1) then NOP in Frame F?

Regards,

Takuya

  • 0
    TI__Mastermind 46975 points

    Hi Takuya,

    1. I guess your are asking the data on SDO in F frame. The answer is, it depends on the command your controller sends o the ADC in the (F-1) frame. 

    •    If  a valid is issued to the ADC in the (F-1), see my answer below for your question 2.
    •    If all other combinations except a valid READ command is issued in frame (F-1), the output data in the frame F will be the latest conversion data converted in "B". Please remember the /CS chip selection signal is also a conversion start signal which will initiate a conversion at the rising edge of each CONVST/CS signal.  

    The content you highlighted is talking about all other combinations in the frame F and the output data word in frame (F+1). You are asking about the output data in the frame F while the NOP command is sent in the same frame F. 

    2. If a valid Read command is issued in the frame (F-1), the output data in the frame F will contain 16-bit or 8-bit register data, followed by 0's. 

    Regards,

    Dale 

  • 0 in reply to Dale Li
    Prodigy 50 points

    Hi, Dale

    Thank you for reply.

    Summary:

    • If a valid READ command issued in the frame (F-1), the output data contains some register data in the frame F. (not the conversion result)
    • If any commands except a valid READ issued in the frame (F-1), the output data is the latest conversion data in the frame F.
      • The "latest" conversion data is the result of CONVST/CS signal between frame (F-1) and F.


    Regard,

    Takuya