How does the Apple Watch accomplish USB-PD over MagSafe?

[38034580]

If I connect an Apple Watch to a charger connected to a USB port with the data ports open, it refuses to charge. However, if I short the data pins, it charges fine. Also, an Apple Watch 8 charger will not destroy an Apple Watch 6 or lower, considering the higher voltage (9V) the S8 uses to charge, due to the charger falling back to low voltage (5V). How does the Apple Watch detect the state of the USB data pins over MagSafe since MagSafe doesn't carry data, and how does the Apple Watch tell the PD enabled charger to "fall back" to 5V over MagSafe?

[Levent]

All USB chargers default to 5v then step up depending on client and host handshake. If there is no data going into the phone, then PD detection is done at the wireless charger.

[38034580]

1 minute ago, Levent said:

All USB chargers default to 5v then step up depending on client and host handshake. If there is no data going into the phone, then PD detection is done at the wireless charger.

@LeventI meant how does the watch "talk" to the brick when MagSafe doesn't do data, as the watch itself is in some way "talking" to the puck or brick?

[Levent]

Just now, 38034580 said:

I meant how does the watch "talk" to the brick when MagSafe doesn't do data?

If all you said is true, simply to guess, it doesnt. All handshaking is done by magsafe charger. I am not familiar with how magsafe works but otherwise I dont see how that can happen.

[Kilrah]

9 minutes ago, 38034580 said:

since MagSafe doesn't carry data

It doesn't provide a data path you can use, but most wireless charging standards can exchange the little bit of data necessary to negotiate charging parameters so it's likely no different there.

[Alex Atkin UK]

3 minutes ago, Kilrah said:

It doesn't provide a data path you can use, but most wireless charging standards can exchange the little bit of data necessary to negotiate charging parameters so it's likely no different there.

There's an example here talking about how QI do it.  Apple will be similar.

 

[WhitetailAni]

On 12/29/2023 at 10:46 AM, 38034580 said:

@LeventI meant how does the watch "talk" to the brick when MagSafe doesn't do data, as the watch itself is in some way "talking" to the puck or brick?

The AW charger isn't MagSafe 3. It predates MagSafe 3 by a fair but. The charging pucks do have data transfer - they have their own firmware that's booted up whenever the device is plugged in, so the puck and the Watch can communicate and negotiate faster charging.

If you connect a charging puck to a Windows computer, you'll see the prompt that "Windows is setting up Apple Watch Charging Cable" or something like that.

[ccnow]

As others have said, there is data being exchanged or inferred between the two devices. There's a reason these things - Magsafe charges for instance - have firmware.

[WhitetailAni]

22 hours ago, ccnow said:

As others have said, there is data being exchanged or inferred between the two devices. There's a reason these things - Magsafe charges for instance - have firmware.

It's kind of funny how many Apple products have firmware.

 

The little Lightning to HDMI and Lightning to VGA adapters (codename Haywire) have a microcontroller in there (the Samsung S5L8747 with 256MB of RAM) and their firmware is loaded from iOS every time it's plugged in. Why?

Lightning cannot provide the signals for HDMI. It instead provides a custom compressed data stream that Haywire has to decompress and convert into HDMI signalling.

[ccnow]

1 hour ago, WhitetailAni said:

It's kind of funny how many Apple products have firmware.

 

The little Lightning to HDMI and Lightning to VGA adapters (codename Haywire) have a microcontroller in there (the Samsung S5L8747 with 256MB of RAM) and their firmware is loaded from iOS every time it's plugged in. Why?

Lightning cannot provide the signals for HDMI. It instead provides a custom compressed data stream that Haywire has to decompress and convert into HDMI signalling.

You act like microcontrollers in other charging devices and adapters aren't a thing? They very much are.