TRF7970A: TRF7970A No Rx IRQ

Mesut TOPUZLU

Intellectual 690 points

Part Number: TRF7970A
Other Parts Discussed in Thread: MSP430FR4133

Hi everyone.

Past several days, I experimented with TRF7970A chip because I am using it on our project.

I think that I progressed a little bit on TRF7970A. But, at some of points I am in stuck. I explained below;

Project parameters : 3v3 power, SPI with SS, 14443A and 106 Kbps

Flow;

1. Enable chip (EN=H);

1. Cast SOFT RESET and IDLE

2. Configure Chip Status Reg

3. Configure ISO Control reg.

4. Configure Regulator reg.

5. Configure Modulator reg (13.56 Mhz crystal)

6. Configure NFC target det. level reg to 0x00 (for errata)

thus far everythin is normal. Am I right?

And then, rf power on, cast REQA.

Observations;

1. On the TX path 13.56 MHz sinusoidal signal (observed with oscilloscope and Vpeak-to-peak 5,5-6V arround)

2. After REQA commands I am receiving an interrupt form TRF, and reading IRQ stat reg.

a. if there is no a tag (Type-A 14443) near the antenna, I see only TX started flag (0x80)

b. if there is a tag (Type-A 14443) near the antenna, I see only TX started and RX started flag. (0xC0). But there is no second interrupt for RX comletion. Why?

c. When tag is near the antenna, after the rx start (but no interrupt), i read FIFO status and there is '2' number. It may be true because ATQA response is 2 byte. Am I right?

d. In FIFO register, there are 0x04 and 0x00 bytes. Are these ATQA response bytes?

Best reagards....

over 6 years ago

0 Ralph Jacobi over 6 years ago

TI__Guru*** 129700 points

Hello Mesut,

In almost all cases the reception of 0xC0 isn't RX in progress, it is TX Complete AND RX Complete. Therefore, there won't be a second interrupt in that case.

If you get a 0xC0 you are servicing IRQ too slow for proper device operation. See Section 4.6 of the FAQ guide for full details on the issues caused by 0xC0 IRQ's: www.ti.com/.../sloa246

The FIFO register may not have accurate RX data if you allow a 0xC0 to occur.

0 Ralph Jacobi over 6 years ago in reply to Ralph Jacobi

TI__Guru*** 129700 points

Hello Mesut,

This Logic Capture of full ISO14443A process for NFC Type 2 Tag may help you as well: https://txn.box.com/s/olqdm8znf9vnta7hqot0b6fnipxlvajn

You can view it with Saleae logic analyzer software from http://www.saleae.com/

0 Mesut TOPUZLU over 6 years ago in reply to Ralph Jacobi

Intellectual 690 points

Thank you for answer Sir.
1. You said that 0xC0 isn't RX in progress, it is TX complete AND RX complete. But in FAQ doc "An IRQ status of 0xC0 indicates that both the TX complete and RX start bits have been set" written.
2. MCU is FR4133 and runs at 8MHz (I verified that) and as upon receiving an interrupt, I serviced it immediately. In ISR routine first line is reset to FIFO direct command.

Any suggestion?

0 Ralph Jacobi over 6 years ago in reply to Mesut TOPUZLU

TI__Guru*** 129700 points

Hello Mesut,

I was a bit rash and didn't explain my comment better. That is the official definition from the datasheet yes. I am speaking from experience in that it is not normal to get 0x40 after a 0xC0, just how the occurrence goes.

The MSP430FR4133 should never have that issue when firmware is coded correctly. I sent an example to you before which you can use for all the drivers required to talk with the device. Are you using that? If not, please do, don't write code from scratch, you will only spend countless hours of time redoing what we already provide. I know it doesn't have application code for ISO14443A, but at least the SPI and Interrupt handling etc. will be robust. Also I can offer a code base which is very similar that does have ISO14443A which you could port in application code for...

You should look at SPI lines and measure timing for interrupt to Reset FIFO Direct Command, and also make sure the Direct Command is sent properly.

0 Mesut TOPUZLU over 6 years ago in reply to Ralph Jacobi

Intellectual 690 points

Hi.
Thank you for help. I tested your code and some codes I found at forums.
I resolved a bit of problems.
Now, I saw ATQA bytes in FIFO and FIFO byte count is 2 when the RFID card near the antenna.
I think, this indicates that my antenna matching/tuning components true (at least) and antenna circuit works. Am I right?
Now problem is related to drawing current. When RF power on the TRF7970A, the current I measured is 700 mA arround. Because my project is battery powered, this current is so hi from supply. it is also written that max current is 150mA with full power and 5V opt. in datasheet.
Question : Is that normal? or may it related to bad antenna tuning? Unfortunately, I am not experienced wtih RF and antennas issue.
Before, a personnel used microwave studio and calculated values of components and ploted antenna. But now, unfortunately, that personnel not working in our firm.

Waiting for helps.

0 Ralph Jacobi over 6 years ago in reply to Mesut TOPUZLU

TI__Guru*** 129700 points

Hello Mesut,

That is definitely not normal. The device should never source anywhere close to that much current, and unless you have an RF field radiating energy onto the antenna coils, the matching/tuning networks would not result in such a draw.

The output is driven from the IC side, not the antenna side, so it doesn't matter if the tuning is off, the current draw would not be higher than spec. The only affect poor matching/tuning would have is how much of the power outputted by the device actually gets turned into radiated RF energy. 150mA is the max current output regardless of tuning/matching.

The only way the antenna could source current into the system is by an RF field injecting it's RF power into the antenna. At the levels you are describing though, that would almost certainly destroy the device so it wouldn't be functioning.

For 700mA current measurement something else must be the root cause.

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TRF7970A: TRF7970A No Rx IRQ