doc: fix typo in README and remove signal path (it's in the schematic)
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README.md
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README.md
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@ -1,4 +1,4 @@
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The USB-C cable tester shows which features USB-C to USB-C cables support.
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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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=======
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@ -6,16 +6,16 @@ purpose
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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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- Standard: this supports USB 2.0 data transfer as well as Power Delivery (PD)
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- Full-Featured: add differential pair used for SuperSpeed data transfer (for USB3, USB4, ...), and sideband use (SBU) for alternate mode or USB 4 data transfer
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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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On top of that, cables can be electronically marked (eMarked).
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Full-Featured cable should be electronically marked, while this in optional for standard cables.
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eMarked cables include a chip 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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Full-Featured cables should be electronically marked, while this in 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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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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Because what is inside of the cable is not indicated on the outside, the cable tester check for the 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, a least not from plug to plug.
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@ -28,15 +28,15 @@ Plug both ends of the USB-C cable in the tester and read the lights:
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- POWER: ensures the VBUS and GND wires are present, required to power a device.
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- USB2: ensures the D+ and D- wires are present, required for USB data transfer (up to at least 2.0).
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- CC/PD: ensures the Connection Control (CC) wire is present, required to determine the plug orientation and for Power Delivery (PD) communication (used for fast charging)
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- Super Speed: ensure the 4 differential pairs are present, required for super speed data transfer (USB3, USB4, ...)
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- SS: ensure the 4 differential pairs are present, required for Super Speed (SS) data transfer (USB3, USB4, ...)
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- SBU: ensures the Side Band Use (SBU) wires are present, used for alternate modes.
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- eMarker: indicated if the cable is electronically marked, required to support 5A/100W power transfer.
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- eMarker: indicates if the cable is electronically marked, required to 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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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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Some USB Power Monitor (UPM) provide this functionality.
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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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mode of operation
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=================
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@ -46,35 +46,29 @@ Here the methods used to test the different capabilities of the cable:
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- POWER: ensures the VBUS and GND wires are present in the cable, required to power a device.
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Although there 4 ground and 4 power pins, there are only 1 ground and 1 power wires.
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The pins are inter-connected in the plugs on each side of the cable.
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Signal path: VCC -> PWR_VBUS (A4, A9, B4, B9) -> LED -> GND_PWR (A1, B1, A12, B12) -> GND
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- SHIELD: ensures the shell of the plugs are connected on both sides of the cable.
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This does not ensure if there is really a shield in the cable, or just a wire.
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It also can't ensure the shell is simply shorted to GND.
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These limitations are outside of the scope of this tester since I haven't seen any cable cheating this way.
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Also, If the cable has a shield, but only connected one plug, this will not be detected.
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Signal path: VCC -> LED -> SHELL/SHIELD -> GND.
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- USB2: ensures the UTP wire are present, used for USB 2.0 data transfer.
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There is only one pair of UTP wire for the Dp and Dn signals using for USB 2.0 communication, connected to A6 and A7 on both sides.
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Since the plug is reversible on both sides, we short the pins to be sure we can test the cable.
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Signal path: VCC -> UTP_Dp (A6, B6) -> LED -> UTP_Dn (A7, B7) -> GND
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- SS: ensures the SuperSpeed (SS) wires are present, for USB3 (and USB4) data transfer.
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There are 4 pairs of wires (SDPxx) used for differentials signals.
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The tester checks if all are present.
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Signal path: VCC -> TXp1 (A2) -> SDPp1 -> RXp1 (B11) -> RXn1 (B10) -> SDPn1 -> TXn1 (A3) -> RXp1 (B11) -> SDPp2 -> TXp1 (A2) -> TXn1 (A3) -> SDPn2 -> RXn1 (B10) -> LED -> TXp2 (B2) -> SDPp3 -> RXp2 (A11) -> RXn2 (SDPn3) -> TXn2 (B3) -> RXp2 (A11) -> SDPp4 -> TXp2 (B2) -> TXn2 (B3) -> SDPn4 -> RXn2 (A10) -> GND
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- SBU: ensures the sideband use (SBU) are present, used for Alternate Modes.
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There are 2 single SBU wires.
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The tester checks if all are present.
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Signal path: VCC -> SBU1 (A8) -> SBU_A -> SBU2 (B8) -> LED -> SBU1 (A8) -> SBU_B -> SBU2 (B8) -> GND
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- CC: ensures the Configuration Channel is present, used for Power Delivery (PD) communication.
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There is one wire going from CC1 on one side of the connector, to CC1 on the other side of the connector.
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Since the plug on both sides is reversible, there are 4 possible permutations.
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This pin is actually used to determine the orientation of the plug, and do the date signal switching on the right pins.
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Signal path: VCC -> CC (A5, B5) -> CC -> CC (A5, B5) -> LED -> GND
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- eMarker: indicates if the cable is electronically marked.
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The detection is the complicated part of this design.
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