TRF7970A: Issues with reliable SPI communication, MSPM0G3507 and TRF7970A

Part Number: TRF7970A
Other Parts Discussed in Thread: MSPM0G3507,

Tool/software:

I've been able to successfully get the TRF7970A started up and can set the initial registers/read all of the expected values, but I seem to be having troubles when attempting to read RFIDs, where the bytes received on the MSPM0G3507 does not appear to always match what is seen on a logic analyzer - in particular when trying to check for an external RF field - I keep getting values back in the 0x0F read where the oscillator bit is not set, and some where it is indicating an RF field where one should not be present. I'm trying to find examples of the mismatches, but I'll have to poke around a bit more to get screenshots of those.

Initial setup/response:

TX:83
RX:00
TX:80
RX:00
TX:8F
RX:00
TX:40
TX:80
RX:00
RX:01
TRF79XXA_CHIP_STATUS_CONTROL (0x00): 01
TX:41
TX:80
RX:00
RX:21
TRF79XXA_ISO_CONTROL (0x01): 21
TX:42
TX:80
RX:00
RX:00
TRF79XXA_ISO14443B_TX_OPTIONS (0x02): 00
TX:43
TX:80
RX:00
RX:00
TRF79XXA_ISO14443A_BITRATE_OPTIONS (0x03): 00
TX:44
TX:80
RX:00
RX:C1
TRF79XXA_TX_TIMER_EPC_HIGH (0x04): C1
TX:45
TX:80
RX:FF
RX:C1
TRF79XXA_TX_TIMER_EPC_LOW (0x05): C1
TX:46
TX:80
RX:FF
RX:00
TRF79XXA_TX_PULSE_LENGTH_CONTROL (0x06): 00
TX:47
TX:80
RX:00
RX:0E
TRF79XXA_RX_NO_RESPONSE_WAIT_TIME (0x07): 0E
TX:48
TX:80
RX:00
RX:07
TRF79XXA_RX_WAIT_TIME (0x08): 07
TX:49
TX:80
RX:00
RX:91
TRF79XXA_MODULATOR_CONTROL (0x09): 91
TX:4A
TX:80
RX:00
RX:10
TRF79XXA_RX_SPECIAL_SETTINGS (0x0A): 10
TX:4B
TX:80
RX:00
RX:87
TRF79XXA_REGULATOR_CONTROL (0x0B): 87
TX:4C
TX:80
RX:00
RX:00
TRF79XXA_IRQ_STATUS (0x0C): 00
TX:4D
TX:80
RX:00
RX:3E
TRF79XXA_IRQ_MASK (0x0D): 3E
TX:4E
TX:80
RX:00
RX:00
TRF79XXA_COLLISION_POSITION (0x0E): 00
TX:4F
TX:80
RX:00
RX:40
TRF79XXA_RSSI_LEVELS (0x0F): 40
TX:50
TX:80
RX:FF
RX:00
TRF79XXA_SPECIAL_FUNCTION_1 (0x10): 00
TX:09
TX:01
TX:0B
TX:01
TX:18
TX:00
TX:40
TX:80
RX:00
RX:00
TRF79XXA_CHIP_STATUS_CONTROL (0x00): 00
TX:41
TX:80
RX:00
RX:00
TRF79XXA_ISO_CONTROL (0x01): 00
TX:42
TX:80
RX:00
RX:21
TRF79XXA_ISO14443B_TX_OPTIONS (0x02): 21
TX:43
TX:80
RX:00
RX:00
TRF79XXA_ISO14443A_BITRATE_OPTIONS (0x03): 00
TX:44
TX:80
RX:00
RX:00
TRF79XXA_TX_TIMER_EPC_HIGH (0x04): 00
TX:45
TX:80
RX:00
RX:C1
TRF79XXA_TX_TIMER_EPC_LOW (0x05): C1
TX:46
TX:80
RX:FF
RX:C1
TRF79XXA_TX_PULSE_LENGTH_CONTROL (0x06): C1
TX:47
TX:80
RX:FF
RX:00
TRF79XXA_RX_NO_RESPONSE_WAIT_TIME (0x07): 00
TX:48
TX:80
RX:00
RX:0E
TRF79XXA_RX_WAIT_TIME (0x08): 0E
TX:49
TX:80
RX:00
RX:07
TRF79XXA_MODULATOR_CONTROL (0x09): 07
TX:4A
TX:80
RX:00
RX:01
TRF79XXA_RX_SPECIAL_SETTINGS (0x0A): 01
TX:4B
TX:80
RX:00
RX:10
TRF79XXA_REGULATOR_CONTROL (0x0B): 10
TX:4C
TX:80
RX:00
RX:01
TRF79XXA_IRQ_STATUS (0x0C): 01
TX:4D
TX:80
RX:00
RX:00
TRF79XXA_IRQ_MASK (0x0D): 00
TX:4E
TX:80
RX:00
RX:3E
TRF79XXA_COLLISION_POSITION (0x0E): 3E
TX:4F
TX:80
RX:00
RX:00
TRF79XXA_RSSI_LEVELS (0x0F): 00
TX:50
TX:80
RX:00
RX:40
TRF79XXA_SPECIAL_FUNCTION_1 (0x10): 40
Booted! Addr: 00

I've tried to verify the signals themselves against the timing diagram from the datasheet: 

Looking at t_ste_lead, clock and duty cycle, lag time, and CS pulse duration between operations - they appear to be within the timing constraints - the connections to ground are rather long in the test setup, however. (CH4: CS, CH3:CLK, CH2: MOSI CH1: MISO)

SPI setup (1MHz):

  • Code is based off of the 

    TRF7970ABP RFID Reader Demo
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  • Noting that in the above, the 0x0F register read shows 0x00 - would expect this to be 0x40 (or something with that bit active). Going to try to set up a polling to wait for that bit to be active (OSC stabile) before finishing the init.

  • Polling for this to become active works - but later the bit seems to disappear.

    Right now, putting this as likely a software issue where read bytes are not getting discarded/handled properly when performing transmits - can see in logs that there is often a stream of TX bytes without corresponding RX - which would mean that the FIFO buffer would be filling up.

  • Hi James,

      Sorry for the late reply as yesterday was a public US holiday.

      Can you reset the FIFO after receiving data? Let me know if this makes a difference. 

     

  • Hi Charles, no worries - I'm bouncing between this on one board, and some TPS6522053 issues on another board. 
    To be clear - this would be issuing the FIFO clear to the TRF7970A, after getting every read? Or just reading the RSSI values?

    Thanks,

    James

  • Hi James,

      I took a snippet of the SPI transactions between the MCU and the TRF. Please look at the places where Reset FIFO is issued. 

      Direct Command   Reset FIFO (0x0F)
    Direct Command Transmission with CRC (0x11)
    Continuous Write Register  
    Data 0x00 TX Length 1 (0x1D)
    Data 0x20 TX Length 2 (0x1E)
    Data 0x02 FIFO I/O (0x1F)
    Data 0x2B FIFO I/O (0x1F)
    Single Read Register    
    Data 0x80 IRQ Status (0x0C)
      Direct Command   Reset FIFO (0x0F)
    Single Read Register    
    Data 0x40 IRQ Status (0x0C)
    Single Read Register    
    Data 0x77 RSSI Levels and Oscillator Status (0x0F)
    Single Read Register    
    Data 0x0F FIFO Status (0x1C)
    Continuous Read Register    
    Data 0x00 FIFO I/O (0x1F)
    Data 0x0F FIFO I/O (0x1F)
    Data 0xD4 FIFO I/O (0x1F)
    Data 0x33 FIFO I/O (0x1F)
    Data 0xDC FIFO I/O (0x1F)
    Data 0x1D FIFO I/O (0x1F)
    Data 0x00 FIFO I/O (0x1F)
    Data 0x00 FIFO I/O (0x1F)
    Data 0x07 FIFO I/O (0x1F)
    Data 0xE0 FIFO I/O (0x1F)
    Data 0x00 FIFO I/O (0x1F)
    Data 0x00 FIFO I/O (0x1F)
    Data 0x3F FIFO I/O (0x1F)
    Data 0x03 FIFO I/O (0x1F)
    Data 0x8B FIFO I/O (0x1F)
      Direct Command   Reset FIFO (0x0F)
    Direct Command Transmission with CRC (0x11)