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ST25RU3993 - Preamble error (-35)

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PKier
Associate

‎2019-02-22 04:00 AM

Hi all! I've got a strange problem during writing data to a tag and inventory (sometimes). I have the Preamble error (-35). This is the result of gen2WriteWordToTag function or st25ru3993TxRxGen2Bytes function during inventory. Idesigned my own hardware based on the Femto v2.1 reader (AMS product).

My settings: Tx one length = 1.83 * Tari, Tari = 6,25us, LF = 160kHz, long preamble, Miller8.

Can you help me?

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Bart Herse
Senior II

‎2019-03-20 01:32 AM

Hello Pawel,

please check your RX wait time register (0x08) setting and compare this time with the T1 (minimum) time defined in the protocol standard.

RX wait time is needed to mute the transient occurring due to the switch from transmission to reception.

But RX wait time should be well defined in order not to extend into the T1 time definition.

If for instance the RX wait time is configured longer then T1 (minimum) you might miss the beginning of the tag response hence leading to a pre-amble error.

Maybe in your case the setting in marginal.

Also have a look at the no response wait time register this should be configured to be somewhat longer than the T1 (max) limit. So if the anti-collision slot is empty not too much time is wasted.

T1 (among other parameters) will be dependent on BLF - in your case = 160 kHz.

In any doubt you can always download the current ST FW and compare the settings used there.

Please make sure that if you are developing a reader for ETSI ruled markets to meet the transmit mask. A safe bet is to use a TARI of 25 µs. A TARI setting of 6.25µs will not meet the ETSI transmit mask at elevated TX power levels.

Cheers,

B

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Bart Herse
Senior II

‎2019-03-20 01:32 AM

Hello Pawel,

please check your RX wait time register (0x08) setting and compare this time with the T1 (minimum) time defined in the protocol standard.

RX wait time is needed to mute the transient occurring due to the switch from transmission to reception.

But RX wait time should be well defined in order not to extend into the T1 time definition.

If for instance the RX wait time is configured longer then T1 (minimum) you might miss the beginning of the tag response hence leading to a pre-amble error.

Maybe in your case the setting in marginal.

Also have a look at the no response wait time register this should be configured to be somewhat longer than the T1 (max) limit. So if the anti-collision slot is empty not too much time is wasted.

T1 (among other parameters) will be dependent on BLF - in your case = 160 kHz.

In any doubt you can always download the current ST FW and compare the settings used there.

Please make sure that if you are developing a reader for ETSI ruled markets to meet the transmit mask. A safe bet is to use a TARI of 25 µs. A TARI setting of 6.25µs will not meet the ETSI transmit mask at elevated TX power levels.

Cheers,

B

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