mov ax, 1680h ;MS-DOS Idle Call
int 2Fh ;Multiplex Interrupt
MS-DOS Idle Call (Interrupt 2Fh Function 1680h) informs the system that the program is idle—for example, waiting for user input. The function permits the system to suspend the idle program temporarily and transfer control to another program.
This function has no parameters.
The function returns the function status in the AL register. If AL is zero, the system supports suspension of idle programs. Otherwise, the system does not support suspension.
Programs should use this interrupt when they are idle. Before using this interrupt, however, a program should use Get Interrupt Vector (Interrupt 21h Function 35h) to ensure that the interrupt-handler address for Interrupt 2Fh is not zero.
This interrupt is nonblocking, meaning the system does not suspend the program unless another program is ready to be run. In most cases, the interrupt returns immediately and the program continues running. To make sure the system can suspend the program, a program that remains idle should repeatedly call the interrupt as part of its idle loop.
Interrupt 21h Function 35h Get Interrupt Vector
Interrupt 28h MS-DOS Idle Handler