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ADS124S08: RESET Pin

Darren (FAE)
Expert 5483 points

Part Number: ADS124S08

1. What will DOUT/SYNC pins be doing when the xRESET pin is low? Was looking at Figure 3 from the datasheet, and the timing tables...but customer is asking about this and I can't find an answer...

2. During standby-mode, when CS pin is low, will DOUT/SYNC pins ever send any kind of data?

Thanks!

Darren

  • 0
    TI__Guru** 113765 points

    Hi Darren,

    See my responses below.

    Best regards,

    Bob B

    Darren (FAE) said:

    Part Number: ADS124S08

    1. What will DOUT/SYNC pins be doing when the xRESET pin is low? Was looking at Figure 3 from the datasheet, and the timing tables...but customer is asking about this and I can't find an answer...[Bob] DOUT/nDRDY is an output pin controlled by CS and the START/SYNC is an input pin.  It is not entirely clear what you are asking for, but the digital input pins should never float and should have a stable logic high or low on the input pin.  This can be set by using a pull-up or pull-down resistor.  As far as the DOUT/nDRDY, which is an output pin, the state of the pin will depend on CS under normal conditions.  The DRDY pin is an always driven output pin.  When in RESET the DRDY pin will go high. 

    2. During standby-mode, when CS pin is low, will DOUT/SYNC pins ever send any kind of data? [Bob] Again it is not clear what you are asking about. Standby differs from power-down.  Standby mode is waiting for the a START command or START/SYNC pin to go high to initiate conversion mode.  See section 9.4 of the ADS124S08 datasheet.  DOUT/nDRDY will be active at the last logic state of the last command action.  So the output could be either high or low.  If a command is issued, such as RDATA or RREG, then the DOUT/nDRDY pin will clock out the data as expected.

    Thanks!

    Darren

  • 0 in reply to Bob Benjamin
    TI__Expert 5483 points

    Hi Bob,

    I took some time to review the request and I think I can clarify.

    1. When xRESET is low, what is the state of the DOUT and SYNC pins?
    - The SYNC pin should have a pullup/pulldown resistor, so will be either logic HIGH or LOW when the xRESET pin gets pulled low - yes?
    - The DOUT is an output, and if xRESET is pulled LOW while CS is HIGH, DOUT stays high impedance - yes?
    - If xRESET is pulled LOW while CS is LOW, DOUT will remain at whatever state (HIGH/LOW) it was driven - yes?
    - If xRESET is pulled LOW, and CS changes state, what will the DOUT pin do?

    2. During standby-mode, if the CS pin is low:
    - The ADS124S08 is waiting for the START command, or START/SYNC pin to go HIGH; when it does, it will start conversion mode - understood☑
    - As such, the DOUT pin is not high impedance, and retains whatever state (HIGH/LOW) it was during the previous action, before standby mode -yes?
    - The SYNC pin is an input, and should be driven low by the MCU, or pulled low via pulldown resistor...and when it goes HIGH, the ADC will leave standby mode and enter conversion mode -yes?

    Thanks,
    Darren

  • 0 in reply to Darren (FAE)
    TI__Guru** 113765 points

    Hi Darren,

    See my responses below.  In some cases I will need to verify with the digital designer, and I will respond again as soon as I can.

    Best regards,

    Bob B

    Darren (FAE) said:

    Hi Bob,

    I took some time to review the request and I think I can clarify.

    1. When xRESET is low, what is the state of the DOUT and SYNC pins?
    - The SYNC pin should have a pullup/pulldown resistor, so will be either logic HIGH or LOW when the xRESET pin gets pulled low - yes? [Bob] As this is an input pin, the state of the input will be controlled externally.  As you said it could be pull-up, pull-down, or controlled by a micro.
    - The DOUT is an output, and if xRESET is pulled LOW while CS is HIGH, DOUT stays high impedance - yes? [Bob]  Yes that should be correct, but I will need to verify with the designer.
    - If xRESET is pulled LOW while CS is LOW, DOUT will remain at whatever state (HIGH/LOW) it was driven - yes? [Bob]  Maybe.  I will have to ask the designer the action of the pin.  Basically the reset takes place on the rising edge of the reset pin.  I agree that it is not clear what the action of the device is while reset is low.
    - If xRESET is pulled LOW, and CS changes state, what will the DOUT pin do?  [Bob]  I will need to ask the designer.

    2. During standby-mode, if the CS pin is low:
    - The ADS124S08 is waiting for the START command, or START/SYNC pin to go HIGH; when it does, it will start conversion mode - understood☑
    - As such, the DOUT pin is not high impedance, and retains whatever state (HIGH/LOW) it was during the previous action, before standby mode -yes? [Bob] Yes.
    - The SYNC pin is an input, and should be driven low by the MCU, or pulled low via pulldown resistor...and when it goes HIGH, the ADC will leave standby mode and enter conversion mode -yes? [Bob] Yes, if the START/SYNC pin is pulled high the ADC will enter conversion mode from the previous state of standby.

    Thanks,
    Darren

  • 0 in reply to Bob Benjamin
    TI__Guru** 113765 points

    Hi Darren,

    Here are the responses from the digital designer:

    - The DOUT is an output, and if xRESET is pulled LOW while CS is HIGH, DOUT stays high impedance - yes?

    [DD] Yes the high impedance state of DOUT is controlled by CSn only. As long as CSn is high DOUT will remain in the high impedance state.


    - If xRESET is pulled LOW while CS is LOW, DOUT will remain at whatever state (HIGH/LOW) it was driven - yes?

    [DD] In this case DOUT will go low. RESET pin resets everything in the device including the SPI interface and output shift register, which in turn causes DOUT to be pulled low


    - If xRESET is pulled LOW, and CS changes state, what will the DOUT pin do?

    [DD] If CSn is transitioning from high to low while reset is low the user will see DOUT going from high-impedance to driven low. If CSn is changing state and going high then user would see DOUT changing from driven low to high-impedance.

    Best regards,

    Bob B