Why does T4.1 USB host have two GND pins?

[Jamewi]

The USB host pins on the Teensy 4.1 are:

• 5v
• D-
• D+
• GND
• GND

Why are there 2 Ground pins? Are they to be treated differently at all or just connected together?

 

[KurtE]

I believe mainly because it matches the pinout of several of the cables and I think the pinouts of some PC boards.

Example cable: https://www.pjrc.com/store/cable_usb_host_t36.html

If you look at schematic of T4.1 (or 3.6) you will see something like:

 

[MichaelMeissner]

The USB host pins on the Teensy 4.1 are:

• 5v
• D-
• D+
• GND
• GND

Why are there 2 Ground pins? Are they to be treated differently at all or just connected together?

IIRC, the cable for USB host is a PC cable used internally in older motherboards. The two grounds were because there was the concept of ground within the device, and true earth ground. I'm a software guy, so I can't tell you the difference between the two.

 

[PaulS]

From the USB 2.0 spec:

6.3 Cable

USB cable consists of four conductors, two power conductors, and two signal conductors.
High-/full-speed cable consists of a signaling twisted pair, VBUS, GND, and an overall shield. High-/fullspeed cable must be marked to indicate suitability for USB usage (see Section 6.6.2). High-/full-speed
cable may be used with either low-speed, full-speed, or high-speed devices. When high-/full-speed cable is
used with low-speed devices, the cable must meet all low-speed requirements.​

So the outer GND pin is meant for the cable shield, the GND pin next to D+ is power GND.



Paul

 

[PaulStoffregen]

When Teensy 3.6 was designed, the goal was compatibility with commonly available PC internal USB2 cables, rather than requiring a new type of cable.