TRF7970A: Are Tx/Rx timeouts documented somewhere?

Hello Koos,

It's a mixture of trial and error and adding buffer times because not all tags reply in the same period of time. This is still a general example code so we don't want to limit it by only assuming the only tags used with it are the ones we have in house to test with.

If you want to be more precise, and believe the tags you are using conform to NFC forum standards, you can look up the official NFC forum specifications for timeouts (or even investigate SLOA227 firmware for timeouts, as that is coded per NFC forum specs).

Also if you know exactly which tags you are using, you can hook on LSA lines onto the SPI channels and measure the time for your tag(s) to reply to each command consistently and then modify the timeouts to fit that.

Dear Koos - 

Assuming you are referring to ISO14443A in general since you refer to Type 2 and Type 4 cards. As you may know, NFC is based on the HF RFID standards and the low level timing specs are located in the ISO standards.

 

the ISO14443-2 has all the bit timings for the PCD (the reader) which the TRF79xxA IC handles. NFC only allows communication at 106kbps for Type A, and the Type 2 NFC cards only do 106kbps, so that would lead you to needing to look at ISO14443-3, to see the specs on the frame delay times allowed between the PCD to PICC (tag) and vice-versa. (this is the time between the end of the last pause transmitted by the PCD and the first modulation edge within the start bit transmitted by the PICC. 

For REQA/WupA, Anticollision and Select commands, the Frame Delay Time (FDT) for the last bit being a 1 is 1236/fc (91uSec) and for the last bit being a 0, it is 1172/fc (86uSec)

all other commands at 106kbps are an integer value >9 x 128 + 84 / fc (for last bit being a 1) or integer value >9 x 128 + 20 / fc

hope this (plus what Ralph said) helps you with understanding the boundary conditions you have to operate with here. Bascially, what you will need to do is go through the flow charts in the standard and add up all the times for what you are doing command/response-wise and that will give you the minimum of what is needed.