INT 21 - DOS 2+ - IOCTL - READ FROM CHARACTER DEVICE CONTROL CHANNEL AX = 4402h BX = file handle referencing character device CX = number of bytes to read DS:DX -> buffer Return: CF clear if successful AX = number of bytes actually read CF set on error AX = error code (01h,05h,06h,0Dh) (see #01680 at AH=59h/BX=0000h) Notes: format of data is driver-specific (also see separate entries below for some specific cases) this function was not supported by Digital Research's DOS Plus SeeAlso: AX=4400h,AX=4403h"DOS",AX=4404h"DOS",INT 2F/AX=122Bh
INT 21 U - MS-DOS 7.0+ - CONFIG$ device - GET CONFIGURATION INFORMATION AX = 4402h BX = file handle for character device "CONFIG$" CX = number of bytes to read (at least 5) DS:DX -> buffer for ??? data (see #01444) Return: CF clear if successful AX = number of bytes actually read CF set on error AX = error code (01h,05h,06h,0Dh) (see #01680 at AH=59h/BX=0000h) SeeAlso: AX=4403h"CONFIG$" Format of MS-DOS 7.0 CONFIG$ ??? data: Offset Size Description (Table 01444) 00h WORD ??? (0000h) 02h WORD ??? (0000h or value read from IO.SYS segment 70h) 04h BYTE ??? (value read from IO.SYS segment 70h)