doc: improve purpose and usage
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README.md
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README.md
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@ -6,25 +6,25 @@ The USB-C cable tester shows which features a USB-C to USB-C cable supports.
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purpose
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purpose
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USB-C cables come in a several flavours.
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USB-C to USB-C cables come in a several flavours.
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The [USB Type-C Cable and Connector Specification](https://www.usb.org/document-library/usb-type-cr-cable-and-connector-specification-revision-21) lists two types of cables:
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The [USB Type-C Cable and Connector Specification](https://www.usb.org/document-library/usb-type-cr-cable-and-connector-specification-revision-21) lists two types of cables:
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- Standard: this supports USB 2.0 data transfer, as well as Power Delivery (PD)
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- Standard: this supports USB 2.0 data transfer, as well as Power Delivery (PD)
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- Full-Featured: this adds differential pairs used for SuperSpeed (SS) data transfer (for USB3, USB4, ...), and sideband use (SBU) for alternate modes or USB4 data transfer
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- Full-Featured: this adds differential pairs used for SuperSpeed (SS) data transfer (for USB3, USB4, ...), and sideband use (SBU) for alternate modes or USB4 data transfer
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On top of that, cables can be electronically marked (eMarked).
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On top of that, cables can be electronically marked (eMarked).
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Full-Featured cables should be electronically marked, while this in optional for standard cables.
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Full-Featured cables should be electronically marked, while this is optional for standard cables.
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eMarked cables include chips that communicate on the CC wire using the PD protocol.
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eMarked cables include chips that communicate on the CC wire using the PD protocol.
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They provide information about the cable, and are mandatory (but not sufficient) for 5A current transfer (e.g. for 100W charging) instead of the standard 3A (e.g. 60W).
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They provide information about the cable, and are mandatory (but not sufficient) for 5A current transfer (e.g. for 100W charging) instead of the standard 3A (e.g. 60W).
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Then there are not specification compliant cables, that only support charging, or no PD communication.
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Then there are not specification compliant cables, that only support charging, or no PD communication.
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I suspect some full-featured cables are not electronically marked, and most magnetic cables are not shielded, at least not from plug to plug.
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Because what is inside of the cable is not indicated on the outside, the cable tester checks for the individual capabilities.
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Because what is inside of the cable is not indicated on the outside, the cable tester checks for the individual capabilities.
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I suspect some full-featured cables are not electronically marked, and non-5A marked cables are sparse.
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And most magnetic cables are not shielded, at least not from plug to plug.
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usage
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usage
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=====
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Ensure a non-empty CR1220 battery is in the tester.
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Plug both ends of the USB-C cable in the tester and read the lights:
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Plug both ends of the USB-C cable in the tester and read the lights:
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<img src="picture/v3_ff.webp" title="Full-Featured cable" height="250"/>
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<img src="picture/v3_ff.webp" title="Full-Featured cable" height="250"/>
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@ -39,7 +39,7 @@ Plug both ends of the USB-C cable in the tester and read the lights:
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Note: the eMarker indication does not mean the cable does support 5A/100W power transfer.
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Note: the eMarker indication does not mean the cable does support 5A/100W power transfer.
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Most of the time, an electronically marked cable does support 5A, since the chip costs more than the wire.
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Most of the time, an electronically marked cable does support 5A, since the chip costs more than the wire.
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This information needs to be read out from the chip inside the cable using the PD protocol.
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But to confirm it, this information needs to be read out from the chip inside the cable using the PD protocol.
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The cable tester does not support this functionality.
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The cable tester does not support this functionality.
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Some USB Power Monitor (UPM) provide this functionality.
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Some USB Power Monitor (UPM) provide this functionality.
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