USB inventor explains why the connector was not designed to be reversible

Re:USB inventor explains why the connector was not designed ... by randyrand on Monday October 09, 2023 @07:24PM (#37826730)

To help visualize:

    1: GND
    2: DATA +/-
    3: VCC
    4: DATA +/-
    5: GND

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Re:USB inventor explains why the connector was not designed ... by userbinator on Monday October 09, 2023 @10:06PM (#37827803)

With that pinout you'd end up with one orientation being full/high-speed and the other being low speed.

Edit: see https://en.wikipedia.org/wiki/USB_communications#Signaling_s...

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Re:USB inventor explains why the connector was not designed ... by anticensor on Monday October 09, 2023 @11:30PM (#37828221)

Would be an acceptable tradeoff.

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Re:USB inventor explains why the connector was not designed ... by kelnos on Monday October 09, 2023 @11:37PM (#37828268)

But when the plug was designed, there was only one speed.

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Re:USB inventor explains why the connector was not designed ... by moring on Tuesday October 10, 2023 @01:15AM (#37828739)

Only if you don't also redefine the convention to select speeds.

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Re:USB inventor explains why the connector was not designed ... by levidos on Monday October 09, 2023 @10:44PM (#37828001)

Can't that square metal be used as ground?

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Re:USB inventor explains why the connector was not designed ... by klysm on Monday October 09, 2023 @11:26PM (#37828198)

You don’t always want the shield coupled to the signal ground. If it’s coupled on both sides then you can have all kinds of fun problems. Ideally, the shield should be connected to the ground on one end

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Re:USB inventor explains why the connector was not designed ... by crote on Tuesday October 10, 2023 @04:57AM (#37829869)

> Ideally, the shield should be connected to the ground on one end

Depends on the signal. With low-frequency stuff (like audio) you want to ground the shield on one side to avoid ground loops, but with high-frequency stuff (USB 3, for example) you definitely want to ground the shield on both sides: if you don't, you end up creating an antenna which is really bad for your EMI performance.

USB 1.x happens to be at an in-between point where neither issue is a big deal. The connector spec literally says "use accepted industry practices", so either approach is fine if it manages to pass emissions testing.

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Re:USB inventor explains why the connector was not designed ... by klysm on Tuesday October 10, 2023 @08:26AM (#37831174)

That goes against all the guidance I’ve read, but I’m an amateur so you may be right. I’m confused on why it relates to signal speed though. For instance, I’ve read that this guidance also applies to Ethernet which is quite high frequency and based on differential pairs

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Re:USB inventor explains why the connector was not designed ... by effie on Wednesday October 11, 2023 @10:17AM (#37844710)

> Question: “I have been told that you should only ground the Ethernet cable at one end. Is this true?”

> Answer: “Sometimes yes, but only if you are seeking to avoid a ground loop. You likely don’t have to worry about this. If you are running shielded Ethernet between two structures that have their own separate AC systems or separate grounding rods installed, then YES, you should worry about what is known as a ground loop. A ground loop occurs when you have actual conflicting AC ground systems. Merely bonding your Ethernet cable at multiple points to the same AC grounding system in a single structure does not create ground loops. Think in terms of ground rods. How many ground rods are involved? If you have more than one with more than one structure involved then you are wise to bond to ground at a single end only.”

From https://www.truecable.com/blogs/cable-academy/residential-bo...

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