ST25RU3993-EVAL board - RSSI values 4-bit or 8-bit?

[ETage.1]

Hi,

I am using the ST25RU3993-EVAL board for distance measurement, and therefore need a adequate resolution on the RSSI values for accuracy. I am using the available SDK for the board. After looking through the datasheet for ST25RU3993, the RSSI values for the I-channel is 4-bits and for the Q-channel is also 4-bit; in the register (RSSI display register, page 67).

However, when i use the Embedded Software for the board, the values range from 0-255, i.e. 8-bit for each I-channel and Q-channel. This is what i would rather use since it has a higher resolution.

How can i get the same values as the Embedded Software? Maybe i am missing a registry address.

Thanks!

Emil T

https://www.st.com/resource/en/datasheet/st25ru3993.pdf

https://www.st.com/en/evaluation-tools/st25ru3993-eval.html#tools-software

[Bart Herse · Accepted solution]

Hi,

ST25RU3993 features a logarithmic RSSI with 4 bit resolution for I & Q.

Log. RSSI can be read out from register 0x2B, but check the configuration bits r2Bpage[0] - r2Bpage[3] in register 0x29 first.

In 0x29 the type of log. RSSI is defined.

Additionally a linear RSSI is available with a 8 bit resolution for I & Q.

Lin. RSSI is acquired through the on-board ADC.

The source for the AD conversion is defined in register 0x10 through bits msel[0] - msel[3].

The result of the AD conversion can be retrieved from the register 0x2D.

Note that register 0x2D is a paged register.

Page selection is done in register 0x29 through bits r2Dpage[0] - r2Dpage[1].

Set the bits r2Dpage[0] - r2Dpage[1] to "00" for ADC result in 0x2D.

When the registers are set correctly the AD conversion can be started by the MCU through the direct command: Trigger AD Conversion (0x87).

Note, in order to get an 8 bit value for I and Q, the AD conversion needs to triggered two times in total.

For each AD conversion, register 0x10 needs to be configured to get I and Q.

Cheers,

B