INT 21 - DOS 1+ - BUFFERED INPUT
AH = 0Ah
DS:DX -> buffer (see below)
Return: buffer filled with user input
Notes:  ^C/^Break checked, and INT 23 called if detected
reads from standard input, which may be redirected under DOS 2+
if the maximum buffer size (see below) is set to 00h, this call returns
immediately without reading any input
SeeAlso: INT 2F/AX=4810h

Format of input buffer:
Offset  Size    Description
00h    BYTE    maximum characters buffer can hold
01h    BYTE    (input) number of chars from last input which may be recalled
(return) number of characters actually read, excluding CR
02h  N BYTEs   actual characters read, including the final carriage return

See also: 210C

210A - DOS 1+ - BUFFERED INPUT