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I am performing electrical validation of EMMC interface using oscilloscope per JEDEC spec. One of the test is to validate setup and hold time for CMD and DATA signal both way (R&W).On scope,I can't tell the difference between data read/write. I was wondering if anyone knows how to tell the difference. Same goes for CMD in vs CMD out.

Many thanks'

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If you have control over the firmware driving the eMMC, generate a sync pulse on an unused (or noncritical) GPIO. Then use this pulse to sync your 'scope to the host; now you can differentiate in/out by how delayed they are from the sync. For example, have the controller generate sync then immediately send a polling command on CMD. Now you can look at that command (CMD out) and immediately following it will be the response (CMD in).

If you don't have access to the firmware, try putting a resistor in series with the signal. The signal will be a slightly lower voltage on the downstream side of the resistor. Experiment with resistor values to find one that produces a detectable voltage drop without trashing the signal too badly. If you're lucky there might already be a resistor in place for noise filtering and you can work with that.

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  • \$\begingroup\$ Excellent suggestion for using a small series resistor. Why didn't I think of that. Many thanks'. \$\endgroup\$ – Judge Judy Feb 9 '16 at 6:28

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