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Channel switching in continuous conversion mode of AD4111

Hello
I have a question about channel switching in continuous conversion mode of AD4111.

Is it possible to disable CH0 and enable CH1 to switch channels while performing continuous conversion with CH0 enabled?

Is it possible to switch channels only at the timing of initialization?

I would be grateful if you could reply.

Best Regards,
Knj

  • Hi, 

    Can you help us clarify the question please?

    In continuous conversion mode the ADC is continously converting sequentially through enabled channel. If your question is if you can switch(enable/disable) channel while the ADC is continuously converting the I guess the answer is yes. You can enable/disable channel any time by writing to specific channel registers. Please take note that everytime you switch channel a settling time is required before a valid conversion can be read so if in case the ADC is still in the process of converting at a specific channel and you forced to switch the channel then the previous conversion will not be complete/invalid so you just need to wait for another conversion equivalent to settling time before you can get a new valid conversion. It is advisable to include the status register when reading the conversion so that you will know which channel the data reading belongs to. 

    It is interesting that you want to enable/disable a channel at a time when the internal automatic sequencer can do the job for you. Is there any specific reason for this? 

    Thanks,

    Jellenie

  • Hi,Jellenie

    thank you for your reply.

    What you mentioned is what I wanted to know.
    If I switch channels while the ADC is running continuous conversion mode, do I need to make the changes according to Figure 35 on page 23 of the data sheet?
    Isn't channel switching completed even if only A in the flowchart is changed? Do B and C need to be written again?

    Best Regards,

    Knj

  • Hi, 

    I guess the suggested flow in the datasheet is to ensure that any channel conversion will not be interrupted every time the channel switch. Because like I said the ADC has an automatic sequencer that perform automatic conversions to all enabled channels. So every time you switch channels or every time you write to channel setup configurations then the conversions will be interrupted. 

    In terms of your question if you need to write this again. For the setup configuration, I think it is not always necessary once you will only need a fixed setup. But for ADC mode it is also okay not to write this again as you are in continuous conversion mode but the benefit of writing this again is at least after you switched channel, writing to ADC mode could also mean initiating a new start conversion useful when you are in single conversion mode. 

    Thanks, 

    Jellenie

  • Hi,

    Thank you for your reply.

    I would like to check the conversion result of CH0 regularly and check CH1 and CH2 occasionally.
    I don't want to reduce the frequency of checking the conversion result of CH0, so basically I want to enable only CH0 and enable only CH1 and CH2 only at a specific timing.

    Enable only CH0 and use it in continuous conversion mode, change 15bit of 0x10 to 0 and change 15bit of 0x11 to 1 at a specific timing.
    Therefore, I am expecting the conversion result of CH1, but I can get the conversion result of CH0.
    Is it possible to change the channel simply by rewriting bit15 of each channel register?

    Best Regards,

    Knj

  • Hi, 

    The sequencer is automatically performed conversions from lower enabled channel to highest enabled channel. So in general you cannot control the channel conversion by just switching the enabled/disabled bit. 

    If you want to really control the start of conversion for each channel, we have this Alternate synchronization feature where in it requires an input to /SYNC to control the start of conversion. When the /SYNC input is taken low, the ADC completes the conversion on the enabled channel, selects the next channel in the sequence, and then waits until the SYNC input is taken high to start the conversion. Setting the ALT_SYNC bit in the interface mode register to 1 enables an alternate synchronization scheme. Though this scheme is only recommended for multiple channels enabled, it is not recommended for single channel only so I guess your scheme will be more complicated as you need to switch the scheme at a specific timing as you have mentioned. 

    Thanks,

    Jellenie

  • Hi,

    Thank you for your reply.

    It turned out that CH can be switched at any timing by setting bit12 of 0x02 to 1 and controlling the SYNC pin.

    I have two questions.


    Question 1
    Enables CH0 to CH3. Use continuous conversion mode.
    Set bit12 of 0x02 to 1 and switch channels with the SYNC pin.
    At this time, CH0 conversion is repeated until the SYNC pin is dropped to low, and if the SYNC pin is dropped to low once, it changes to CH1, and if it is dropped to low twice, it changes to CH2. Is this correct?

    Question 2
    In SYNC pin control, can the order of CH switching be done only in order from the smallest number?
    Is it possible to intentionally select and switch channels like this? (Example: CH0 → CH1 → CH0 → CH3 → CH2 → CH0)

    I would be grateful if you could reply.

    Best Regards,
    Knj

  • Hi, 

    1. Yes, When /SYNC pin is taken low the conversion on the current enabled CH0 will be completed, once completed the data is written to the data register and then the sequencer will moved to the next enabled channel. When the sequencer moves to the next enabled channel the modulator and digital filter are then held in a reset state until the pin is taken high again. Please take note that it is necessary to complete the conversion including the updates on the register before it will switch to the channel. So in general the SYNC pin controls the start of conversion but not really control the switching of the channels. 

    2. No, But since the ADC offers up to 16 channels you can make use of the extra channels and just mirror the required channel for measurements. I am not sure if it is clear but what I am saying is for example is you can plan the sequence and utilize the other remaining channels to meet your target sequence of measurements. 

    Thanks,

    Jellenie

  • Hello

    Thank you for your reply.
    Since the CH to be converted is not repeated, I understand that it is difficult to mirror another channel.

    I understand that it is better to use a simultaneous sampling ADC when the channel switching is in random order, but the AD4111 has only one channel enabled as a means of switching specific channels in order. Is there no choice but to sample, reset once, then configure the ADC according to the flow on P23 and enable another channel?

    I would be grateful if you could reply.

    Best Regards,
    Knj

  • Hi, 

    You do not always need to configure the channel if you can use different setup configuration for each. The part has 8 dedicated setup register that can be use to any channel register settings. So you can just initialize the setup configuration for each channel and then you can just manually switch the channel according to your needs. 

    If you can provide the details on what exactly you wanted to do then I can help you with the flow. 

    Thanks,

    Jellenie

  • Hi,

    thank you for your reply.

    The specific things I want to do are as follows.

    ① I want to sample CH0 basically. Sometimes sample another channel.
    ② In single conversion mode
    CH0 × 15 times → CH3 × 1 time → CH1 × 1 time → CH3 × 1 time → CH0 × 15 times → CH2 × 1 time
    I want to sample like this.


    I would be grateful if you could tell me specifically what procedure should be used for initialization and which register should be changed.
    I'm sorry I don't understand.

    Best Regards,
    Knj