[S32K3] SQI (Signal Quality Indicator) value test

[Sungbhin-Oh]

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?

[PavelL]

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