17-08-2015, 16:46
A few new scope traces, with more appropriate measurements.
MOSI:
SCK:
DC:
Observations: Amplitude measurements seem entirely reasonable. Overshoot on the 5V line ranges from 14.9% to 18.6% (0.7 to 0.87 volts). Overshoot on the 3.3V output ranges from 22.4% to 31.3% (0.80 to 1.03 volts). Overshoot is measuring only the low-to-high transition, not the high-to-low transition. Thus, overshoot is higher both in relative (percent of amplitude) and absolute (number of volts) terms on the output of the level shifter.
I'm not at all saying this is the problem--I don't know enough to suggest that. It just looks a bit anomalous to me.
MOSI:
SCK:
DC:
Observations: Amplitude measurements seem entirely reasonable. Overshoot on the 5V line ranges from 14.9% to 18.6% (0.7 to 0.87 volts). Overshoot on the 3.3V output ranges from 22.4% to 31.3% (0.80 to 1.03 volts). Overshoot is measuring only the low-to-high transition, not the high-to-low transition. Thus, overshoot is higher both in relative (percent of amplitude) and absolute (number of volts) terms on the output of the level shifter.
I'm not at all saying this is the problem--I don't know enough to suggest that. It just looks a bit anomalous to me.