More about the Raspberry Pi’s USB ports

A Little More about the Raspberry Pi’s USB Ports
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Raspberry Pi

The older Raspberry Pi B models come standard with 4 USB ports. Even so, it only has one root USB port where all traffic is funnelled too. It operates at a maximum speed of 480mbps (USB 2.0).

Raspberry Pi USB port speed

Global USB specification defines three device speeds –- low-speed (USB 1.1 – 1.5mbps), full-speed (USB 1.1 – 12mbps), and high-speed (USB 2.0). The Raspberry Pi defaults to high-speed.

It is said that there are generally no issues with connecting multiple high-speed USB devices at the same time, but my own experience tells me that there are soft limitations on the number of simultaneously active low- and full-speed devices.

Changing the port speed

In some cases one might need to change the USB port speed for older hardware to full-speed (i.e. USB 1.1) use:

sudo nano /boot/cmdline.txt

and appending the following:

dwc_otg.speed=1

to the very end of the line.

Power requirements

Another important thing about the Raspberry Pi USB ports is that they will only supply 100 mA per port.

This means that “low-power” devices like USB drives, keyboards and mice will work sufficiently, but if you start to get abnormal behaviour, like devices stopping without a reason, brownouts and/or unexpected resets, you should probably get an external USB hub with its own power supply.

Devices such as Wi-Fi adapters, USB hard drives and USB pen drives are known to consume much more than 100mA. It is also noteworthy that in order to supply even low-power devices with sufficient current, the Pi should also be supplied with a proper power supply.

The people at the Raspberry foundation recommends 5V with at least 1.2A (1200mA).

5V 2.5A Power Supply With On/Off Switch (US, EU)
5V 2.5A Power Supply With On/Off Switch (US, EU)
For Raspberry Pi 2/3
Input 100-240V AC. 75x41x29mm. Micro-B USB connector.
Available from BangGood
CanaKit 5V 2.5A Raspberry Pi 3 B+ Power Supply (US)
CanaKit 5V 2.5A Raspberry Pi 3 B+ Power Supply (US)
For Raspberry Pi 2/3
UL Listed. Input >100V AC. 3.75 x 2.75 x 1.25 inches. Micro-B USB connector.
Available from Amazon.com
Official 5.1V 3A Raspberry Pi 4 Power Supply (US)
Official 5.1V 3A Raspberry Pi 4 Power Supply (US)
For Raspberry Pi 4
UL Listed. White. Input: 100-240V 50/60Hz 0.5A, Output: 5.1-3.0A. 3.27 x 2.4 x 1.93 inches. USB-C connector.
Available from Amazon.com

Effect of overclocking

I have heard somewhere that when the Raspberry Pi is overclocked, it will supply less Amperage.

The Raspberry Pi

To get started with the Raspberry Pi you will need the following:

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