2-pads printer ink chip?

[bitwelder]

I was recently replacing the toner cartridge of my Oki laser printer.

Looking at the 'smart' ink chip on it, it's a 6-pins SMD chip (SOIC-6 perhaps?) with only 2 pins connected
to external pads on the tiny PCB.

With only 2 terminals, how does in general such a chip work?
Is the exchanged data encoded in the supply voltage, or does it communicate
in some other way, e.g. a Hall (or other magnetic field) sensor?

[ebastler]

One solution is commercially available as "1-Wire", by Dallas Semiconductor.
https://en.wikipedia.org/wiki/1-Wire

It charges a capacitor to buffer the supply voltage while serial data communications are underway.

[daqq]

There are a few standards that allow communication and power over a single wire + GND. 1 Wire or the Microchip standard:
http://ww1.microchip.com/downloads/en/DeviceDoc/AT21CS01-AT21CS11-Data-Sheet-DS20005857D.pdf

There are actually crypto authentication devices that enable single wire communication, can't remember which devices, designed precisely for this situation.