Function 05H (5): Nondestructive Read

The nondestructive read function applies only to character devices, and in block devices it should do nothing except set the done flag. It returns the next character that would be obtained with a read function (command code 4), without removing that character from the driver's internal buffer. MS-DOS uses this function to check the console driver for pending Control-C characters during other operations.

The nondestructive read function is called with

RH + 2 BYTE Command code = 5

It returns

RH + 3 WORD Status

If busy bit = 0, at least one

character is waiting

If busy bit = 1, no characters are

waiting

RH + 13 BYTE Character (if busy bit = 0)