Hi Tech,
We use TRF7970A in our products. At power up, upon doing the ISO-15693 Inventory, the TRF reader responds with a Tag UID. All TRF readers work fine, except for one TRF Reader. The issue is MOST of the time the reader has no Tag UID to report even the Tx and Rx are completed during the Inventory process on POWER UP. And when the TRF Reader goes into this state, subsequent inventory commands behave the same way.
Here is the sequence of our ISO15693 Inventory.
1. MCU sends ISO-15693 Inventory command.
2. Reader responds with Tx Complete IRQ.
3. MCU resets FIFO.
4. Reader responds with Rx Complete IRQ with No Error.
5. MCU reads FIFO Status to find out number of bytes in FIFO.
Good case: 11 bytes
Bad case: 0 bytes
We use SPI (with SSEL) to interface with the TRF7970A. One slot inventory (same problem with 16 slots). Our MCU is NXP1767. We have tried with different ISO15693 Tags but still experiencing the problem.
So I wonder if the intermittent problem is due to a bad TRF Reader or something else? We verified the SPI timing on the scope.
Thanks.
Charlie