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RF430FRL15X Biopatch schematic question

Zoltan
Prodigy 100 points


Dear All,

My question: why R4 pull down resistor (10k) is in the schematic of the Biopatch application?

Q1: I'm suppose the chip has internal pull up / pull down resistors, do I miss something here? 

Q2: Does R4 has to be mounted for JTAG connection?

Q3: Does R4 has to be mounted when only RF communication goes on and no JTAG connection at all?

Thank you!

Zoltan

  • 0
    TI__Expert 7820 points

    Zoltan Doczi said:
    Q1: I'm suppose the chip has internal pull up / pull down resistors, do I miss something here? 

    The resistor is needed for the internal ROM firmware to determine is there is a host controller present or a digital sensor.  Essentially if the pin is pulled low the ROM code will configure the eUSCI for slave operation and handle the host communication internally.  Please see Table 23 in the RF430FRL15xH Firmware Users Guide for more on how to configure the device.

    Zoltan Doczi said:
    Q2: Does R4 has to be mounted for JTAG connection?

    This resistor is not needed for JTAG operation but should not disturb the communication given that it is such a high value resistance.   Just make sure that the JTAG connection is happening on the trace before the resistor.

    Zoltan Doczi said:
    Q3: Does R4 has to be mounted when only RF communication goes on and no JTAG connection at all?

    For this schematic this resistor is not needed to be connected if host controller is not used or a digital sensor is not connected.  The ROM code will sample this pin on power-up and randomly choose a configuration.  It is important to not choose the digital sensor option and have P1.0,P1.1,P1.2,P1.3 tied to ground because the ROM code will (when a P1.7 is pulled high - digital sensor option) will drive these pins high.  When powering the device from RF this short circuit will prevent the device from powering up. 

    Generally this resistor is needed for any non-JTAG operation.  However if you are not using the ROM code (NFC only project or total custom project) then this resistor is not needed.