Serial Decode
Measuring VBUS @ PS_RDY
According to the USB-PD specification, the PS_RDY Message shall be sent by the Source (or by both the new Sink
and new Source during the Power Role Swap sequence or Fast Role Swap sequence) to indicate its power supply
has reached the desired operating condition.
Follow these steps to set up the decoder to make the VBUS @ PS_RDY measurement.
1. Probe CC using one channel and VBUS using a second channel. In this example, CC is on C1and VBUS is on
C2, which are entered in the corresponding fields on the Decode Setup dialog.
2. On the USB-PD subdialog, select the PS_RDY_LEVEL checkbox.
3. You can optionally also trigger on the PS_RDY Message by selecting it from the Trigger dialog. In this case,
the oscilloscope will trigger on the first instance of PS_RDY in the USB-PD stream, placing it at the top of the
decoder result table.
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