Int 21H [1.0] Function 0BH (11) Check input status

[1] Checks whether a character is available from the keyboard.

[2.0+] Checks whether a character is available from the standard input device. Input can be redirected.

Call with:

AH = 0BH

Returns:

AL = 00H if no character is available

FFH if at least one character is available

Notes:

[1] If a Ctrl-C is detected, an Int 23H is executed.

[2.0+] If the standard input is not redirected, and a Ctrl-C is detected at the console, an Int 23H is executed. If the standard input is redirected, a Ctrl-C is detected at the console, and BREAK is ON, an Int 23H is executed.

If a character is waiting, this function will continue to return a true flag until the character is consumed with a call to Int 21H Function 01H, 06H, 07H, 08H, 0AH, or 3FH.

This function is equivalent to IOCTL Int 21H Function 44H Subfunction 06H.

Example:

Test whether a character is available from the standard input.

.

.

.

mov ah,0bh ; function number

int 21h ; transfer to MS-DOS

or al,al ; character waiting?

jnz ready ; jump if char ready

.

.

.