5 ms·
Some of this wrong, some of this is way too wordy. > USB-C cables that support Power Delivery 2.0 and 3.0 can carry a minimum of 7.5 watts (1.5 amps at 5 volt
by chx 5y ago
Some of this wrong, some of this is way too wordy.
>
USB-C cables that support Power Delivery 2.0 and 3.0 can carry a minimum of 7.5 watts (1.5 amps at 5 volts) or 15W (3A at 5V), depending on the device, cable, and purpose.
Nope, all USB C cables are 60W minimum. The connector might support less, but the cables do support 60W minimum.
> USB-C Charge Cable—designed in the early days of USB-C
Nope, nothing wrong with a USB C cable which doesn't have the high speed lanes connected. That's a perfectly specification conformant cable. High speed lanes is the phrase I miss from this too long article.
Here's a much shorter explanation of it all.
A USB C cable always have separate wires for 1) power , either 60W or 100W capable. The latter needs an eMarker IC in the connector 2) a separate pair for 0.48Mbit/s speed USB data (aka USB 2.0) 3) it can have and most do have four high speed lanes (each lane is formed from two wires as differential pairs). These lanes can carry various data , by default it will use two lanes to carry USB data -- at at least 5gbps, if the cable is short enough then 10gbps. (While 20gbps mode over four lanes is defined so few hosts support this we don't need to care.) There are alternative modes besides USB, namely DisplayPort and Thunderbolt. In DisplayPort alternate mode it can use 2 or 4 lanes for DisplayPort. If two then the other two can be used for USB data as above. DisplayPort has its own versions: DisplayPort 1.2 can deliver 8.64 Gbit/s video data over two lanes, while 1.3/1.4 can carry 12.96 Gbit/s and for both double that over four lanes. (DisplayPort 1.4 introduces compression as well which needs to be supported by the monitor and it's very rare to do so.) This is aggregate video bandwidth for PCs: they can drive multiple monitors using a DisplayPort technology called MST. For Mac, you need Thunderbolt.
Thunderbolt. Unlike the previous ones where the cable is functioning the same as a pre-USB C cable and a simple (basically, passive converter) can dole out USB and DisplayPort data this one is a complex bus and both ends needs to have a Thunderbolt controller. The Thunderbolt 3 bus can carry PCI Express and DisplayPort data (USB is provided by the controller presenting a hot plug root hub, due to hot plug nature there's a bevy of problems), the Thunderbolt 4 bus can carry PCI Express and DisplayPort and USB data. (Footnote: Thunderbolt 4 is the same as USB 4 with some optional features made mandatory. It is somewhat unlikely we will see non-TB4 USB 4 controllers so this is mostly just pedantry -- you can treat USB 4 and TB4 as being the same.) The bus bandwidth in one direction depending on cable length can be 20gbps or 40gbps. When allocating this bandwidth, DisplayPort has priority. How much DisplayPort is on the bus in total is a bit confusing due to some history: laptops with one Thunderbolt port most often will only put one DisplayPort 1.2 connection on the bus. Laptops with two ports always have full Thunderbolt and will put two DisplayPort connection on the bus (very rarely, single port laptops will do this too, mostly early workstations). This confusion goes away in Thunderbolt 4, that's always full. But the bus is never faster than 40gbps so even if it is fed by two DP 1.3/1.4 connections, it still can't deliver more than 40gbps data where two independent DisplayPort cables would be able to deliver slightly more than 50gpbs.
Finally, power. If only 5V is required, resistors are used to signal how much power is requested. For 9/15/20V power is negotiated: the devices figure out which one is source and which one is sink, once that's done, the source will communicate how much power it is able to provide. At most 3A can be used normally, at 20V provided the right cable is present, 5A is also a possibility. There is a separate wire for this communication. Using the same communication process, the data roles are decided: one of them will be upstream (think host) one of them will be downstream (think peripheral). There's a sensible default where the upstream data role takes on the source power role but this can be changed using this negotiation.
Footnote: these were fixed power. Today some devices support the PPS (Programmable Power Supplies) feature which allows the sink to rapidly change the wattage as needed. This also requires eMarker cables.
And yes, cables are a mess. https://people.kernel.org/bleung/how-many-kinds-of-usb-c-to-usb-c-cables-are-there https://people.kernel.org/bleung/how-many-kinds-of-usb-c-to-...
- ggm 5y agoIf the standards are adhered to.
- AnonHP 5y agoMy eyes glazed over looking through your comment. I think you and the author of the article are in agreement as far as this part of the article is concerned: “What we want is to look at a port and cable and know what they do. That shouldn’t be so hard, but it apparently is.”
- chx 5y agoI believe, as I wrote elsewhere in the past the solution would've been standardized introspection: cheap devices you can plug into a port / a cable into and it gives capabilities.
- genewitch 5y agoYour last point there, if someone wants a real example, the DJI drone remote controls are a peripheral that provides power to a phone, when you connect your phone to it, the phone starts charging and launches the app.
- ximeng 5y agoThis still confuses me. Are you saying: A. Cable physically consists of: 1. 60/100W power wire pair 2. USB2 speed data wire pair supporting 0.48Mbit/s 3. 2/4 high speed data wire pairs (“high speed lanes”), normally 4 Each high speed lane supports at least 5/10Gbit/s depending on cable length. 4. Separate wire for negotiating power supply and data host and peripheral 5. eMarker cables are required for rapidly changing wattage of power supply (Programmable Power Supplies, PPS) Note that two DisplayPort cables (not USB-C) could support 50gbps, more than a USB-C maximum of 40gbps. B. Protocols (all over high speed lanes apart from USB2): 1. USB2 2. USB3 (by default using two high speed lanes at 10gbps, four high speed lanes at 20gbps theoretically possible but rarely supported by hosts) USB requires negotiation of host and peripheral (upstream and downstream). 3. DisplayPort 1.2 (8.64Gbit/s video data over 2 high speed lanes) / DisplayPort 1.3/1.4 (12.96Gbit/s over 2 high speed lanes, double over 4). MST technology allows splitting the aggregate video data bandwidth across monitors. DisplayPort 1.4 supports video compression, but this is rarely supported by monitors. If using only 2 high speed lanes the other 2 can be used for USB data. 4. ThunderBolt 3/4 (needed for Mac video). ThunderBolt 4 is USB4 with optional features mandatory, however in practise these optional features are likely to always be included so they can be treated as the same. C. Device support: 1. Power: 5/9/15/20V. Requirements signalled by resistors on the device side if only 5V. More than 5V negotiated between devices: 1. Agree source and sink, by default the data upstream/host is source but this can be negotiated, 2. Source indicates how much power it can provide, either 3A or with a 20V cable optionally 5V. This assumes fixed power, some devices now support PPS. 2. Data bus types: 1. passive (supports USB and DisplayPort) / 2. ThunderBolt 3 (PCI Express and DisplayPort, USB as hot-plug root hub(?)) / 3. ThunderBolt 4 (PCI Express, DisplayPort, USB) ThunderBolt controllers needed on both sides to support ThunderBolt. 3. Bus bandwidth is maximum 40gbps. If cable is long bandwidth may only be 20gbps. Laptops with one ThunderBolt port typically support DisplayPort 1.2 bandwidth on the bus, laptops with two ThunderBolt ports support two DisplayPort 1.2 bandwidth. (There is some distinction between “full” and “non-full” ThunderBolt that goes away in ThunderBolt4.)