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TRF7970A with AVR?

Mitar Simic
Prodigy 10 points
Other Parts Discussed in Thread: TRF7970A

Dear all,

I am working on my student project AVR microcontroller based RFID system with  TRF7970A. I want to have SPI communication without SS. I read data sheet so I am not sure is this correct configuration for my purposes:

Vss_pa, Vs_rx, Vss, Vss_a, I/O_1, I/O_2 should be connected to GND

Vin, EN should be connected to Vdd

I/O_7 is MOSI: I/O_6 is MISO: DATA_CLK is SCK from mcu

ASK/OOK is for choosing ASK or OOK

I not sure for purposes pins IRQ and MOD. I am confused how tp manipulate with them... IRQ should generate external interrupt to my AVR when tag is detected? What about MOD?

Thanks in advance

  • 0
    TI__Guru* 91206 points

    So you want to use an Atmel MCU? :) Where are you going to school? Maybe our university relations folks would love to chat with your faculty so they can help convert your engineering dept over to MSP430, LM4F, etc....

    Anyway - with regards to your question, as i know the tool chain you are using maybe cannot be swapped out right now and it sounds like you have a project to finish...

    The IRQ line is indeed the interrupt back to the MCU to indicate something has occurred. The reading of the IRQ status register is then the pointer to the logic of what to do next. For example, after transmitting out a command sequence to a tag, you will get an IRQ which needs to be serviced by reading the IRQ status register (which clears the IRQ), then most likely you would have an 0x80, telling you that the transmission was successful (we call EOTX (end of transmit) IRQ)...then you would next get an IRQ, which would for example be 0x40, indicating an EORX (end of recieve) has occured, then you would read the FIFO status for # of bytes to clock out, then read the FIFO for the data...you can see in the data sheet the descriptions of the IRQ register and and some examples, too. (see the TRF7970A DS, section 5.9.xx)

    The ASK/OOK line in your case most likely can just be pulled to GND or you can connect it to a GPIO on your MCU like we have it shown in the reference schematics. MOD same thing, unless you are using any Mifare Classic tags, then you would need control of the MOD pin for Direct Mode 0, so then it would need to be connected to a GPIO. 

    Usually we are recommending connecting EN line to a GPIO, with a pulldown (needs to see low to high transition) so you can have control of some of the power modes...EN2 can also be connected to a GPIO or pulled high or low, depending on your need for even lower power consumption.

    Correct about I/O_0, I/O_1 and I/O_2 being at GND potential for SPI w/o SS.

    If it helps here is a schematic of SPI with SS, which you can modify for your own usage, since you say you want to do without SS. (I/O_3 and I/O_5 are connected in this drawing as well, and this is for Special Direct Mode, which you may or may not need, depending on which tags you are trying to use here - normally not needed, just FYI)

    7183.TRF7970A_SPI_MSP430F2370_dongle_sch.pdf

     

      

  • 0 in reply to Josh Wyatt
    TI__Guru* 91206 points

    one more thing...the schematic i just put up - does have one error - the VDD_X line does need the bypass caps on it too - just like VDD_A, Bandgap, etc....

  • 0 in reply to Josh Wyatt
    Prodigy 10 points

    Actually, now that I've had a look myself I would be interested in porting this over to Arduino too. It would be a nice little project - not that much code.

    If anyone else is interested please post here.