4 ms·

A-A cables do exist. I came across it with a USB 3.0 hard drive. But the version 3 micro-B connector was notoriously fragile, so this one had a sturdier A conne

A-A cables do exist. I came across it with a USB 3.0 hard drive. But the version 3 micro-B connector was notoriously fragile, so this one had a sturdier A connector instead.

actionfromafar 5y ago
Those are not standard though, more like a "hack".
- masklinn 5y ago
  They’re beyond non-standard, they’re explicitely against standard: A-A cables are actively hazardous, because the A side is the one which provides power, and USB hosts usually don’t expect to get powered through the cable (though I hope and expect over time they added protections for that as USB got misused). B-B cable (whether full, mini, or micro) is at least innocuous and inert.
  - fmajid 5y ago
    And that's also the reason why C female to A male adapters are banned, otherwise you could attach them on both ends of a C-C cable to make an A-A cable.
  - tjoff 5y ago
    Though they are often not just a cable. But a chip inside the cable, presumably acting as slave for both hosts - and I guess fully compliant in theory at least.
    - masklinn 5y ago
      > and I guess fully compliant in theory at least. An A-A cable is necessarily non-compliant by definition.
      - tjoff 5y ago
        Why? In practice it would be equivalent to a device with two say micro-usb-ports. Unusual for sure, but necessarily non-compliant?
        masklinn 5y ago
        > Why? Because the official spec says so, and as described above USBx was originally a strictly host-device protocol, the A plug is at the host, and the B plug is at the device. An A-A cable is a host-host link, which from the USB standpoint doesn't make sense (pre type-C). In particular, the host is in charge of sending power, the device is supposed to be able to handle it. In particular if one of the hosts gets powered off, its 5V now gets powered (possibly without limitation) by the other, drawing way more than the 500mA specified by the spec, and damaging the cable if you're lucky (until that catches on fire and burns down your house) or the electronics (and killing your mobo). Think of it as creating a plug-plug extension cord and connecting two of your house's outlets together (don't do that). > In practice it would be equivalent to a device with two say micro-usb-ports. micro-USB has both A and B variants (likewise mini). What you're probably thinking of is a micro-B plug. And having a B-B cable is also not compliant though nobody does it because it's completely useless (because the device side is "passive", so nothing can happen). > Unusual for sure, but necessarily non-compliant? Yes necessarily non-compliant. [0] "Smart" devices like smartphones and tablets can be both device and host which created an issue, this was acknowledged and support was added with "On The Go" (OTG) and mixed-compatibility receptacles (so USB mini and micro have AB receptacles, aka female, which can thus accept either an A plug — acting as host — or a B plug — acting as device). OTG cables are still asymmetric, with an A side and a B side, and A-A cables are still illegal OTG. Type C replaces this with a fully symmetrical cable.
        tjoff 5y ago
        I feel like you haven't read a single word I've written. Please reread my original comment. Imagine two usb-to-serial adapters. Now, imagine connecting them to different PCs. Now connect a serial cable between those two adapters. That is what I'm describing. Only the usb-to-serial-adapters are actually inside the cable. No USB host is talking directly to another USB host. No USB host is "powering" another USB host etc. Your comments are not relevant to the scenario described.
watermelon0 5y ago
Many USB switches come with A-A cables for connecting to computers. The only reason I could find is that B connectors are a bit higher, so they would need to use a larger case.

A-A cables do exist. I came across it with a USB 3.0 hard drive. But the version 3 micro-B connector was notoriously fragile, so this one had a sturdier A connector instead.

actionfromafar 5y ago

Those are not standard though, more like a "hack".

masklinn 5y ago
They’re beyond non-standard, they’re explicitely against standard: A-A cables are actively hazardous, because the A side is the one which provides power, and USB hosts usually don’t expect to get powered through the cable (though I hope and expect over time they added protections for that as USB got misused). B-B cable (whether full, mini, or micro) is at least innocuous and inert.
- fmajid 5y ago
  And that's also the reason why C female to A male adapters are banned, otherwise you could attach them on both ends of a C-C cable to make an A-A cable.
- tjoff 5y ago
  Though they are often not just a cable. But a chip inside the cable, presumably acting as slave for both hosts - and I guess fully compliant in theory at least.
  - masklinn 5y ago
    > and I guess fully compliant in theory at least. An A-A cable is necessarily non-compliant by definition.
    - tjoff 5y ago
      Why? In practice it would be equivalent to a device with two say micro-usb-ports. Unusual for sure, but necessarily non-compliant?
      - masklinn 5y ago
        > Why? Because the official spec says so, and as described above USBx was originally a strictly host-device protocol, the A plug is at the host, and the B plug is at the device. An A-A cable is a host-host link, which from the USB standpoint doesn't make sense (pre type-C). In particular, the host is in charge of sending power, the device is supposed to be able to handle it. In particular if one of the hosts gets powered off, its 5V now gets powered (possibly without limitation) by the other, drawing way more than the 500mA specified by the spec, and damaging the cable if you're lucky (until that catches on fire and burns down your house) or the electronics (and killing your mobo). Think of it as creating a plug-plug extension cord and connecting two of your house's outlets together (don't do that). > In practice it would be equivalent to a device with two say micro-usb-ports. micro-USB has both A and B variants (likewise mini). What you're probably thinking of is a micro-B plug. And having a B-B cable is also not compliant though nobody does it because it's completely useless (because the device side is "passive", so nothing can happen). > Unusual for sure, but necessarily non-compliant? Yes necessarily non-compliant. [0] "Smart" devices like smartphones and tablets can be both device and host which created an issue, this was acknowledged and support was added with "On The Go" (OTG) and mixed-compatibility receptacles (so USB mini and micro have AB receptacles, aka female, which can thus accept either an A plug — acting as host — or a B plug — acting as device). OTG cables are still asymmetric, with an A side and a B side, and A-A cables are still illegal OTG. Type C replaces this with a fully symmetrical cable.
        tjoff 5y ago
        I feel like you haven't read a single word I've written. Please reread my original comment. Imagine two usb-to-serial adapters. Now, imagine connecting them to different PCs. Now connect a serial cable between those two adapters. That is what I'm describing. Only the usb-to-serial-adapters are actually inside the cable. No USB host is talking directly to another USB host. No USB host is "powering" another USB host etc. Your comments are not relevant to the scenario described.

watermelon0 5y ago

Many USB switches come with A-A cables for connecting to computers. The only reason I could find is that B connectors are a bit higher, so they would need to use a larger case.