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DLP-7970ABP: Modulation and guard time in ISO14443B tags

Part Number: DLP-7970ABP
Other Parts Discussed in Thread: TIDA-00217, RF430CL330H, TRF7970A

Hello,

I was through the Firmware designed to Interface DLP-7970ABP and MSP430G2 Launch pad. I came across these lines to communicate with ISO14443B tags in nfc_appISO14443B()

 

TRF79xxA_setupInitiator(0x0C); // Configure the TRF79xxA for ISO14443B @ 106kbps

// When a PICC is exposed to an un-modulated operating field

// it shall be able to accept a quest within 5 ms.

// PCDs should periodically present an un-modulated field of at least

// 5.1 mSec duration. (ISO14443-3)

// *NOTE* Guard time extended to 10 milliseconds in order to support passively

// powered RF430CL330H designs such as seen in TIDA-00217.

MCU_delayMillisecond(10);

if (ISO14443B_sendPollCmd(REQB,0)) // Issue REQB Command with 1 slot to start

{

bTagFound = true;

}

I believe that the TRF79xxA_setupInitiator(0x0C) turns on the RF field with 10%ASK. Aren't we exposing the PICC to the modulated Signal (10%ASK and 13.56Mhz) for 10ms? Where is the field beoming unmodulated again? Are we doing a soft reset before the MCU_delay()?  

  • Hello Manoj,

    The TRF7970A emits an unmodulated RF field until it transmits data. I verified this by comparing a few different settings for Modulator Control and measuring the RF field using an o-scope and pickup coil combo and saw no difference in the RF field prior to commands being sent.
  • Manoj to help with a visual of what you should see - as Ralph's description is 100% correct ==> 

    from the ISO standard, you will see top right behavior for the bits themselves, when the field is modulated

    here is actual - as you can see the field is unmodulated prior to the command, as per the standard requires