This detailed information covers some I/O ports that are not detailed

elsewhere.

Note: All IN and OUT examples are for 8-bit I/O

(e.g., OUT 70H,0 really means MOV al,0; OUT 70H,al)

Port  Description

000H-

01fH  DMA (Direct Memory Access) controller          See DMA Ports

020H-

03fH  Interrupt Controller.  See Interrupt Controller Ports

040H-

043H  8253 Timer chip.                               See Timer Ports

060H  PC/XT  (Programmable Peripheral Interface) port A.  Read keyboard:

IN   al,60H  ;fetches most recent scan code.   See INT 09H

See Scan Code

AT keyboard data register.                     See AT Keyboard

061H-

063H  PC/XT PPI Command/Mode Register.  See PPI Ports.

064H  AT keyboard command register.  This port communicates with the 8042

which runs an on-chip control program for the keyboard.  It accepts

command codes and data bytes.

For commands and programming details, See AT Keyboard

070H  AT register address (write-only) for Real-Time Clock and CMOS RAM.

070H  AT NMI mask.  Use this port to mask the Non-maskable Interrupt.

An OUT with bit 7=0 enables the NMI; with bit 7=1 disables NMI:

OUT  70H,2dH  ;enable NMI--2dH is a reserved addr in the CMOS Memory

OUT  70H,0adH ;disable NMI

080H  AT page register used during POST to accumulate errors

081H-

08fH  DMA page registers                             See DMA Ports

0a0H  PC/XT  NMI mask. Enable/disable Non-maskable Int (RAM parity err)

OUT  0a0H,80H  ;enable NMI

OUT  0a0H,0    ;disable NMI

0c0H-

0dfH  AT DMA controller access to 16-bit DMA         See DMA Ports

0f0H  AT 80287 latch clear.  'Busy' gets latched upon an unmasked 287 error.

OUT  0f0H,0  ;clears the latch

0f1H  AT 80287 Reset.  Coprocessor is reset from protected mode to real mode

OUT  0f1H,0  ;resets the 80287 to real mode

0f8H-

0fcH  AT 80287 data. 286 sends opcodes & operands and receives results.

170H-

177H  AT hard disk controller #2                     See AT Hard Disk Ports

1f0H-

1f7H  AT hard disk controller #1                     See AT Hard Disk Ports

210H  XT Expansion chassis control port

213H  XT Expansion chassis enable

215H  XT Expansion chassis data bus register

215H  XT Expansion chassis address register (high byte)

216H  XT                                    (low byte)

278H-

27fH  Parallel Printer Adapter #2                    See Printer Ports

2e8H-

2efH  Asynchronous Communications Adapter COM4.      See Serial Ports

2f8H-

2ffH  Asynchronous Communications Adapter COM2.      See Serial Ports

320H-

32fH  XT hard disk controller.                       See XT Hard Disk Ports

2c0H-

2cfH  Enhanced Graphics Adapter (EGA) #2.            See EGA I/O Ports

378H-

37fH  Parallel Printer Adapter #1                    See Printer Ports

3b4H- Monochrome Display Adapter (MDA) display control ports.

3baH  See CGA I/O Ports for a summary of usage of the 6854 CRT controller.

The MDA has few capabilities beyond it's single standard display mode.

3bcH-

3bdH  Parallel Printer on MDA                        See Printer Ports

3b0H-

3dfH  Video Graphics Array (VGA)                     See VGA I/O Ports

3c0H-

3dfH  Enhanced Graphics Adapter (EGA)                See EGA I/O Ports

3d2H-

3dcH  Color/Graphics Adapter (CGA)                   See CGA I/O Ports

3e8H- asynchronous communications adapter COM3.

3efH                                                 See Serial Ports

3f0H-

3f7H  diskette drive controller (aka FDC)            See FDC Ports

3f8H- asynchronous communications adapter COM1.

3ffH                                                 See Serial Ports

See Also: I/O Port Map

BIOS Data Area

Interrupts and BIOS Services

Cables and Pin Outs

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