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MSP430FR2533: Captivate - calculate of mutual capacitive sensor number

David M. Alter
Guru 61235 points
Part Number: MSP430FR2533

MSP430 Team,

The MSP430FR2533 datasheet SLAS942B page 2 lists the members of the device family:

QUESTION: How is the number of mutual-capacitive sensors computed?

I thought it was the largest multiplying combination of sensor channels.  So for example, 16 self-capacitive sensors indicates 16 sensor channels.  Hence, you would get 8x8=64 mutual capacitive channels.  But, the FR2533 lists only 16 mutual capacitive sensors despite have 16 sensor channels.  Also, the FR2532 lists only 8 mutual-capacitive sensors despite having 8 sensor channels.  What am I missing?

Regards,

David

  • 0
    TI__Expert 5490 points
    Hello David,

    You are correct that the largest multiplying combination of sensor channels indicates the max number of mutual capacitance buttons and this table you saw in the datasheet shows the typical max number of buttons for each device. When talk about the typical max number of buttons we also consider the SRAM memory size because that is where the sensor data is stored at.

    Since FR2533 only has 2kB SRAM so we recommend the typical max number of buttons to be 16. The same reason apply to FR2532.
    For more information on how to select the CapTIvate device please see the device family section in Technology Guide:
    software-dl.ti.com/.../ch_device.html

    Please let me know if you have any questions.

    Thanks,
    Yiding
  • 0 in reply to Yiding Luo
    TI__Guru 61235 points

    Thank you for your reply Yiding.

  • 0 in reply to Yiding Luo
    TI__Guru 61235 points

    Bleh.  Hit post earlier before I meant to.

    Thank you for your reply Yiding.  I suspected it might have something to do with the amount of RAM.  But then, FRAM can be used as RAM so doesn't this minimize the memory differences between, say, FR2533 and FR2633?

    Also, FR2533 with 2KB SRAM supports 16 mutual sensors, but doubling to 4KB SRAM on FR2633 quadruples the number of mutual sensors to 64?

    Thanks and regards,

    David

  • 0 in reply to David M. Alter
    TI__Expert 5490 points
    Hello David,

    Sorry for the late reply.
    You are correct that FRAM can be used as RAM but the trade-off is that you will lose the FRAM space for your other application code.

    To answer your second question, the number we put in the datasheet is for typical max number of buttons but you are correct that for FR2533 with 2KB SRAM you can do more than 16 mutual sensors and it also depends on the size of your application code.

    Here is some memory size benchmark you can refer to and should give you much better idea on the memory requirement:
    software-dl.ti.com/.../ch_library.html

    Please let me know if you have any questions.

    Thanks,
    Yiding

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