Connecting USB devices in parallel

In summary, the conversation discusses the possibility of connecting multiple USB devices in parallel by connecting their power supply and data lines together. However, it is mentioned that USB drivers are not "tri-state" and may cause conflicts between the devices. The conversation also mentions that I2C is a better option for parallel connections as it releases data lines when not in use. The conversation ends with a question about why I2C is not used more widely.
  • #1
I_am_learning
682
16
Since USB are a kind of Data buses I thought you can simply connect multiple usb devices such as say a keyboard and a mouse in parallel.
I mean, strip out the USB cable of both keyboard and mouse, connect together the Power supply (V+ and V-) and also connect together datas lines (D+ and D-). Then, plug the joined (paralled) device into a single USB port.
Would this work? Why?
 
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  • #2
The drivers for the data lines on USB devices are not "tri-state", so they always "power" the I/O lines. If you connect two data wires directly together they will fight each other and whomever is the strongest will (probably) take precedence. The strongest may not be the device you want to talk to at the time however...

I just looked inside a USB hub and each data line is separate. The particular device has a glob of goop over the "magic-connection" site for the data lines so I'd assume that there is some kind of buffer there which arbitrates which input gets to talk to the output when.

Other serial busses, like I2C, can be "wire-ORed" together because they release the data lines when not in use. I don't know why USB isn't like that come to cogitate on it...
 
  • #3
I thought the data lines were highZ most of the time and the USB devices were in Reading (waiting ) state most of the time for the Host to order them to transfer data. Seems like I am confusing it with I2C.

Thanks for your respones.

Looks like I2c is the winner? Why not use them everywhere?
 

1. How many USB devices can be connected in parallel?

The number of USB devices that can be connected in parallel depends on the type of USB hub being used. A standard USB 2.0 hub can support up to 127 devices, while a USB 3.0 hub can support up to 127 devices per controller. However, for optimal performance, it is recommended to connect no more than 3-4 devices in parallel.

2. What is the benefit of connecting USB devices in parallel?

Connecting USB devices in parallel allows for multiple devices to be connected to a single host computer, allowing for efficient data transfer and minimizing the need for multiple ports. It also allows for devices to be connected and disconnected without disrupting the functionality of other devices.

3. Can all types of USB devices be connected in parallel?

Yes, most USB devices can be connected in parallel as long as they are compatible with the USB hub being used. This includes devices such as keyboards, mice, printers, external hard drives, and more.

4. How do I know if I need a powered USB hub for connecting devices in parallel?

If you plan on connecting multiple high-powered devices, such as external hard drives or scanners, it is recommended to use a powered USB hub to ensure sufficient power for all devices. You can also check the power requirements of your devices and compare them to the power output of the USB hub.

5. Are there any potential issues with connecting USB devices in parallel?

One potential issue with connecting USB devices in parallel is a decrease in data transfer speeds. This is because all devices connected to the same hub share the same bandwidth. Additionally, if one device malfunctions, it can potentially disrupt the functionality of other devices connected in parallel.

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