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doc: improve purpose and usage

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King Kévin 2022-09-09 13:16:24 +02:00
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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.
purpose
=======
USB-C cables come in a several flavours.
USB-C to USB-C cables come in a several flavours.
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:
- Standard: this supports USB 2.0 data transfer, as well as Power Delivery (PD)
- 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
On top of that, cables can be electronically marked (eMarked).
Full-Featured cables should be electronically marked, while this in optional for standard cables.
Full-Featured cables should be electronically marked, while this is optional for standard cables.
eMarked cables include chips that communicate on the CC wire using the PD protocol.
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).
Then there are not specification compliant cables, that only support charging, or no PD communication.
I suspect some full-featured cables are not electronically marked, and most magnetic cables are not shielded, at least not from plug to plug.
Because what is inside of the cable is not indicated on the outside, the cable tester checks for the individual capabilities.
I suspect some full-featured cables are not electronically marked, and non-5A marked cables are sparse.
And most magnetic cables are not shielded, at least not from plug to plug.
usage
=====
Ensure a non-empty CR1220 battery is in the tester.
Plug both ends of the USB-C cable in the tester and read the lights:
<img src="picture/v3_ff.webp" title="Full-Featured cable" height="250"/>
@ -39,7 +39,7 @@ Plug both ends of the USB-C cable in the tester and read the lights:
Note: the eMarker indication does not mean the cable does support 5A/100W power transfer.
Most of the time, an electronically marked cable does support 5A, since the chip costs more than the wire.
This information needs to be read out from the chip inside the cable using the PD protocol.
But to confirm it, this information needs to be read out from the chip inside the cable using the PD protocol.
The cable tester does not support this functionality.
Some USB Power Monitor (UPM) provide this functionality.