TMS320F280025: Can ADC/AIO pins be used as ecapture pins

Hi Lu,

The unused ADC/AIO can be used as an option for eCAP pins.  In the schematic below, eCAP sources can be configured through ECCTL0[INPUTSEL] which is a 128:1 mux:

Any GPIOs can be chosen as eCAP inputs through input crossbar so you would have to configure the INPUTSEL[15:0] to select the INPUT XBAR as source for eCAP.  You would then have to  configure INPUT_XBAR_REG to point to the unused AIO (only supports GP Input function) that you are planning to use for channels belonging to GPIO group H (channels 224 - 247), see datasheet for corresponding ADC/AIO mapping) and adding a note to follow the guidance in TRM section 18.3 on GPIO input qualification.

One final thing: The ADC specifications may be impacted especially if there are IO activities (with high slew rate) adjacent to ADC channels so it would be best to quantify the impact of using the AIO for eCAP purposes while ADC is converting.

Best regards,

Joseph

Hi Joseph:

     If I stagger the AIO pins which used as ecapture pins with the noraml ADC pins,for example,I separate the AIO pins group for eCAP  and the normal ADC pins group with an unused ADC pin,So they are not adjacent now.I want to know whether the impact of using the AIO for eCAP purposes while ADC is converting still exists?

Hi Lu,

That could work but it would still be best to evaluate the impact on ADC conversions.  Issue is not just adjacent pins.  The ADC inputs have to pass through the input mux, where there could be a potential signal coupling.  Reducing the slew rates of the digital signals you intend to pass through the analog inputs as AIO i think would be the better solution.

Best regards,

Joseph

Hi Joseph:

     At the present,I used AIO pins to read the level of pulse and I calibrated the width of pulse through softerware algorithm.I separate the AIO pins group and the normal ADC pins group with an unused ADC pin.Does this solution still have an impact on ADC conversion?I want to use AIO pins for eCAP because I want to simplify the software and reduce the pressure of software.Also the eCAP can increase the accurancy of the calibration of pulse width.