[S32K3] SQI (Signal Quality Indicator) value test

Sungbhin-Oh — Wed, 18 Jun 2025 01:40:34 GMT

Board used: S32K3X4EVB-T172
Test purpose: SQI changes depending on Ethernet cable status

We are currently using the S32K3 EVB board to measure SQI depending on the Ethernet cable status. We are conducting Ethernet communication using a damaged cable and measuring the SQI during the process, but the measured SQI values are only 0 or 7.

How can we observe changes in SQI values (e.g., 1 to 6)?

Are there any application notes or guidance related to SQI values?

Re: [S32K3] SQI (Signal Quality Indicator) value test

PavelL — Thu, 19 Jun 2025 06:03:30 GMT

Hello @Sungbhin-Oh ,

Please find my suggestion below:

1. Use Passive Components

Add resistors or capacitors between the differential pairs (e.g., TX+ and TX−) or to ground.
Example: A resistor of 100–300 Ω between TX+ and TX− can simulate impedance mismatch and reduce signal quality.

2. Untwist or Misalign Cable Pairs

Untwist a portion of the twisted pair (e.g., 5–10 cm) to increase crosstalk and reduce signal integrity.
This can help simulate moderate degradation without complete link failure.

3. Use Long or Low-Quality Cables

Try cables longer than 100 meters or low-grade Cat5e/Cat6 cables with poor shielding.
These naturally introduce attenuation and noise, which may result in intermediate SQI values.

4. Introduce EMI (Electromagnetic Interference)

Place the cable near a noise source like a switching power supply, motor, or RF emitter.
Alternatively, inject noise using a signal generator if available.

5. Use Attenuators or RF Simulators

If you have lab equipment, RF attenuators or cable simulators can precisely control signal degradation.
This allows for reproducible SQI testing across the full range (0–7).

SQI measurement is performed continuously and filtered using a low-pass filter. Therefore, we recommend reading the SQI value no more frequently than once every 10 to 100 milliseconds.

Best regards,

Pavel