If register DH does not contain 00H, control returns to the program with the carry flag set and error code 0001H (invalid function) in register AX.Sets certain flags for a handle associated with a character device. This subfunction may not be used for a handle that is associated with a file.
Call with:
AH = 44H
AL = 01H
BX = handle
DX = device information word
Bit(s) Significance
0 1 if standard input
1 1 if standard output
2 1 if NUL device
3 1 if clock device
4 reserved (0)
5 0 to select ASCII mode
1 to select binary mode
6 reserved (0)
7 1, indicating a device
8—15 reserved (0)
Returns:
If function successful
Carry flag = clear
If function unsuccessful
Carry flag = set
AX = error code
Notes:
If register DH does not contain 00H, control returns to the program with the carry flag set and error code 0001H (invalid function) in register AX.
Bit 5 of the information word for a handle associated with a character device signifies whether MS-DOS considers that handle to be in binary ("raw") or ASCII ("cooked") mode. See Notes for Int 21H Function 44H Subfunction 00H.
Example:
Place the standard output handle into binary ("raw") mode. This speeds up output by disabling checking for Ctrl-C, Ctrl-S, and Ctrl-P between each character.
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; get device information
mov ax,4400h ; function & subfunction
mov bx,1 ; standard output handle
int 21h ; transfer to MS-DOS
mov dh,0 ; force DH = 0
or dl,20h ; set binary mode bit
; set device information
mov ax,4401h ; function & subfunction
int 21h ; transfer to MS-DOS
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