Head substrate, liquid discharge head, and liquid discharge apparatus

A head substrate including a liquid discharge element for discharging a liquid, the head substrate comprising:

• a functional unit configured to realize a discharge detection function that detects that the liquid is discharged, and a digital temperature detection function that detects a temperature of the head substrate;
• and
• a communication input unit to which communication data is to be inputted,
• wherein the communication data includes a bit for not transmitting data for setting the discharge detection function, a bit for not transmitting data for setting the digital temperature detection function, a first portion for setting a function of the functional unit, and a second portion for controlling a supply of current to the functional unit.