Thermal inkjet printhead with de-clog firing mode

A printhead IC comprising:

• an array of nozzles, each with a corresponding heater;
• and,
• drive circuitry for generating drive pulses that energize the heaters, the drive circuitry being configured to operate in two modes, a printing mode in which the drive pulses generated are printing pulses, and a maintenance mode in which the drive pulses generated are a series of sub-ejection pulses preceding a de-clog pulse;
• wherein,
• the printing pulses heat the heaters to form a first vapor bubble in printing fluid that causes ejection of a drop of the printing fluid through the nozzle, the de-clog pulse has lower power and a longer duration than the printing pulses so as to heat the heaters to form a second vapor bubble in the printing fluid which does not cause drop ejection, and the sub-ejection pulses have lower power than the printing pulses and a shorter duration than the de-clog pulse so as to heat the heaters without sufficient energy to nucleate a bubble in the printing fluid.