HSC
Hexadecimal Sequential Coding: An in-band tone signalling protocol comprising 16 tone states.
Ten tone states represent decimals 0-9, a NOTONE, a Repeat tone, a Group tone, an address/DATA frame delineator,
plus Reset and control, totaling 16 tone-coded logic states.
HSC operation is predicated on a decoding technique able to detect tones in random order.
These must be contained within a frame preceded and concluded by NOTONE.