Information Technology Reference
In-Depth Information
Microsoft C++ uses the equivalent _
inp()
function (which is prototyped in
conio.h
).
Inputting a word from a port
The assembly language command to input a word is
IN AX,DX
where
DX
is the data register which contains the address of the input port. The 16-bit
value loaded from this address is put into the register
AX
.
For Turbo/Borland C the equivalent function is
inport()
. Its general syntax is as follows:
value=inport(PORTADDRESS);
where
PORTADDRESS
is the address of the input port and
value
is loaded with the 16-
bit value at this address. This function is prototyped in the header file
dos.h
.
For Turbo Pascal the equivalent is accessed via the
portw[]
array. Its general syntax is as
follows:
value:=portw[PORTADDRESS];
where
PORTADDRESS
is the address of the input port and
value
is the 16-bit value at
this address. To gain access to this function the statement
uses dos
requires to be
placed near the top of the program.
Microsoft C++ uses the equivalent _
inpw()
function (which is prototyped in
conio.h
).
Outputting a byte to an I/O port
The assembly language command to output a byte is
OUT DX,AL
where
DX
is the data register which contains the address of the output port. The 8-bit
value sent to this address is stored in register
AL
.
For Turbo/Borland C the equivalent function is
outportb()
. Its general syntax is as fol-
lows:
outportb(PORTADDRESS,value);
where
PORTADDRESS
is the address of the output port and
value
is the 8-bit value to
be sent to this address. This function is prototyped in the header file
dos.h
.
For Turbo Pascal the equivalent is accessed via the
port[]
array. Its general syntax is as
follows:
