* Translation between USB PD and whatever communication protocol runs on the center Magsafe pin (in Magsafe 1 and 2 it was Dallas 1-wire)
* Disabling power output when the cable is not connected to a computer, so that a metal object touching the spring pins can't create a dangerous short circuit
> What could possibly be the use for any sort of logic in such cable be, given that on both ends of it there’s already a computer as well?
Maybe because MacBooks can be charged via both USB-C and MagSafe connector it forms part of the safety mechanism against frying your motherboard and/or against arcing during connection/disconnection. Especially on the higher-end of the spectrum (e.g. 16-inch MacBooks with 140W MagSafe).
Sort of like the same way electric car chargers handshake before throwing amps down the cable.
The MagSafe connector only has three distinct contacts (there are five pins, but it's mirrored), so there has to be some protocol translation between USB PD and the single control signal used in MagSafe.
Just been scratching my head about this. Then I thought, is it just so they can detect authentic Apple cables and scold you for using an inauthentic one? Because iOS definitely does that. Some kind of challenge/response thing that requires a full Turing machine maybe.
Another thought was something to do with monitoring current or degradation but I cant see why they couldn’t do the same things from either the computer in the power adaptor or the computer in the actual computer.
