Busses, Interrupts and PC Systems - Computer Busses - page 72

Table 2.8 Typical isolated I/O memory map

Address Device

000h-01Fh DMA controller

020h-021h Programmable interrupt controller

040h-05Fh Counter/Timer

060h-07Fh Digital I/O

080h-09Fh DMA controller

0A0h-0BFh NMI reset

0C0h-0DFh DMA controller

0E0h-0FFh Math coprocessor

Hard disk (Secondary IDE drive or CD-ROM drive)

170h-178h

1F0h-1F8h Hard disk (Primary IDE drive)

200h-20Fh Game I/O adapter

Expansion unit

210h-217h

278h-27Fh Second parallel port (LPT2:)

2F8h-2FFh Second serial port (COM2:)

300h-31Fh Prototype card

378h-37Fh Primary parallel port (LPT1:)

380h-38Ch SDLC interface

3A0h-3AFh Primary binary synchronous port

3B0h-3BFh Graphics adapter

3C0h-3DFh Graphics adapter

3F0h-3F7h Floppy disk controller

3F8h-3FFh Primary serial port (COM1:)

Inputting a byte from an I/O port
The assembly language command to input a byte is

IN AL,DX
where DX is the data register which contains the address of the input port. The 8-bit value
loaded from this address is put into the register A

For Turbo/Borland C the equivalent function is inportb() . Its general syntax is as fol-
lows:

value=inportb(PORTADDRESS);

where PORTADDRESS is the address of the input port and value is loaded with the 8-
bit value from 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:

value:=port[PORTADDRESS];

where PORTADDRESS is the address of the input port and value the 8-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.