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ADS7845: wrong DOUT output value

Fanbin Meng
Expert 8735 points
Part Number: ADS7845

Tool/software:

Hi team,

My customer use the ADS7845 for the first time, below is the schematic:

They have two questions:

1. How to handle the PENIRQ pin? should we connect this signal to the host MCU? please help further explain this, thanks.

2. After the customer write the DIN code, they get different output when they haven't touched the RTP screen, why this happened?

Best regards

Fanbin

  • 0
    TI__Mastermind 46535 points

    Hi Fanbin,

    1) The PENIRQ pin can be connected to processer to trigger an interrupt that a measurement is being made on the touch screen. From the data sheet, "When the panel is touched, the PENIRQ output goes LOW, due to the current path through the panel to GND, initiating an interrupt to the processor."

    2) If measurement is taken when no one is touching the screen, you may be getting intermittent connections between the wiper panel and the resistive panel creating unpredictable results. The idea is that once PENIRQ triggers an interrupt, the processor will send the command code to take the measurement. At this point, the users finger should be making contact between the wiper and the resistive panel, creating a more reliable measurement. If there is no finger on the screen then the Wiper pin is floating or making intermittent contact with the resistive panel leading to unpredictable outcomes.

    Best regards,
    Jeff McPherson