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Connecting TRF7970A EVM to a different MCU (e.g. At91SAM7X)

mhr456
Intellectual 295 points
Other Parts Discussed in Thread: TRF7970A

Hello,

I am trying to disconnect TRF7970A chip from MSP430 (on EVM board) and connect it to AT91SAM7X controller. I have performed the steps mentioned below so far.

1. Remove 0 ohm resistors between HDR_4 and HDR_5.

2. Remove resistors R10 (to stop power supply to MSP430).

3. Remove R25, R26 and R27.

4. Connect I/O_0 and I/O_1 to ground and I/O_2 to VDD_I/O. (As I want to use SPI without slave select). MOSI and MISO are also connected to the MCU.

5. Providing DATA_CLK from MCU.

V_IN is connected externally to +5V supply.

The problem appears when the +5V supply is provided, the MSP430 still gets the power (in spite of removing R10 from the board). Additionally, the SPI data is not detected at MOSI.

Why is the MSP430 powers up while it is disconnected from the NFC chip? (Note: EN2 and EN are connected as shown in the schematic.)

Any help is highly appreciated. Thank you very much in advance. :-)

Best regards.

  • 0
    Prodigy 150 points

    Hi Mihir.

    I'm having the exact same challenge  - to disconnect the TRF7970A from the internal MCU on the EVM, and I'm also a bit confused with all the voltages.

    I have a question for you -

    how are you going to connect the EN pin to the external MCU? It is crucial to the activation of the TRF7970A.

  • 0 in reply to Aviv Eben
    Intellectual 295 points

    Hi Aviv,

    Somehow, I disconnected the NFC chip from MSP430 using a bit unconventional method. I had to cut the lines EN, SYS_CLK and DATA_CLK going to MSP430. Because, even if the resistor R10 was removed, MSP430 powered up. By cutting those lines, I totally disconnected MSP430 from the NFC chip.

    Then I connected the line EN to VIN on HDR_2. But, the problem with MOSI line still persists. I am testing the connection and trying to send some data to MOSI of the NFC chip from MCU. But as soon as I connect the MOSI of the MCU to the MOSI of TF7970, the data disappears (MOSI goes to logic low). Are you going to use SPI without SS?

  • 0 in reply to mhr456
    Prodigy 150 points

    I'm going to use SPI with ss, but this is only a matter of connecting ss line to the MCU via HDR_5.

    The real issue here is connecting EN, which has no accessible terminal, to the MCU. How did you manage to do it?

    SYS_CLK and DATA_CLK are accessible via HDR_1, so I guess if the msp430 is off, you don't have to physically cut them off the msp430.


    And, about the power - where does your Vin come from? USB? 

    I need to use the external MCU's power to supply the Vin for the nfc, which makes things even more complex...


    About your MOSI - did you define the MOSI on your MCU correctly? Did you  define NFC's I/O 0-2 correctly?

  • 0 in reply to Aviv Eben
    Intellectual 295 points

    Hey,

    - I used a thin wire and solder it to the node of R24 where it is connected to EN and then connect it to VIN on HDR_2.

    - I had to cut the line DATA_CLK because when I connect the DATA_CLK(of NFC chip) to the DATA_CLK (of MCU), it was causing the MSP430 to power up. I confirmed it by checking the voltages.

    - I am not using USB to power up the board. I connected external +5V to the VIN on HDR_2.

    - And about my MOSI, I have connected it correctly (I checked the connection many times). I connected I/O_0 and I/O_1 to ground, I/O_ 2 to VDD_I/O. I am using SPI w/o SS.

    I checked (with the oscilloscope) that data is available at MOSI of the MCU and when i connect it to the MOSI (I/O_7) of the chip, it disappears.

  • 0 in reply to mhr456
    Prodigy 150 points

    Maybe it has something to do with syncing the MOSI with DATA_CLK?   (5.9.5.1 in the trf7970a user guide)

  • 0 in reply to Aviv Eben
    Intellectual 295 points

    I think that is also okay. I still don't know what the problem is.

  • 0
    Intellectual 310 points

    I remove the R10 and R11. I can send Direct command and write and read the RAM registers, but I had a problem with the clock polarity, what I write is different that I read, but I can change the clock on SYS_CLK pin, so my write routine must be right.