INT 21 - Attachmate Extra - SET HOST WINDOW STATE
AH = A2h
AL = set status byte
bit  7  : 0=power off, 1=power on
bit  6  : 0=not installed, 1=installed
bits 5-3: reserved
bits 2-0: window number 1-4=host B-E

See also: 21A1

21A2 - Attachmate Extra - SET HOST WINDOW STATE