I/O Port Map
• Ports 000H-0ffH are reserved for and used by the system board
• Ports 100H-3ffH are decoded on the I/O bus for use by adapter cards
• Ports 400H and up are not available on the system bus
The following table summarizes I/O port usage for the PC/XT and AT.
Individual ports covered in greater detail are marked with a hyperlink.
Additional info is covered in I/O Port Detail. See Cables and Pin Outs
for info on hardware connectors.
AT PC/XT Description More Information
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000-01f 000-00f DMA controller #1, 8237A-5. DMA Ports
020-03f 020-021 Interrupt controller, 8259A. Int Controller
040-05f 040-043 Timer 8253-5 (AT: 8254.2). Timer Ports
060-063 PPI (Programmable Peripheral Interface) PPI Ports
keyboard, equipment switches, timer
060-06f Keyboard controller 8042 AT Keyboard
070-07f Real-time clock, CMOS Memory, NMI mask CMOS Memory
080 manufacture's diagnostic checkpoint
080-09f 080-083 DMA page register 74LS612 DMA Ports
0a0 NMI (Non-maskable Interrupt) mask
0a0-0bf Interrupt Controller #2, 8259A
0c0-0df DMA controller #2, 8237A-5 DMA Ports
0f0-0ff Math Coprocessor
102 PS/2 Programmable Option Select
170-177 Hard disk (secondary) AT Hard Disk Ports
1f0-1f7 Hard disk AT Hard Disk Ports
200-207 200-20f Game I/O (joystick A/D port) Joystick Port
210-217 Expansion Box
278-27f 278-27f Parallel Printer #2 (#3 with MDA) Printer Ports
2c0-2df 2c0-2df EGA #2 EGA I/O Ports
2e8-2ef Asynchronous Adapter Port #4 Serial Ports
2f8-2ff 2f8-2ff Asynchronous Adapter Port #2 Serial Ports
300-31f Prototype card
320-32f Hard disk XT Hard Disk Ports
370-377 Diskette Controller (secondary) FDC Ports
378-37f 378-37f Parallel Printer #1 (#2 with MDA) Printer Ports
380-38f 380-38f Synchronous Data Link Control (SDLC)
3a0-3af 3a0-3a9 Bisynchronous port #1
3b0-3df 3b0-3df Video Graphics Array (VGA) VGA I/O Ports
3b0-3bf 3b0-3bf Monochrome Display Adapter/Printer #1 Printer Ports
3c0-3cf 3c0-3cf Enhanced Graphics Adapter (EGA) #1 EGA I/O Ports
3d0-3df 3d0-3df Color/Graphics Adapter (CGA) and EGA CGA I/O Ports
3f0-3f7 3f0-3f7 Diskette controller FDC Ports
3ef-3ff Asynchronous Adapter Port #3 Serial Ports
3f8-3ff 3f8-3ff Asynchronous Adapter Port #1 Serial Ports
See Also: I/O Port Detail
BIOS Data Area
Interrupts and BIOS Services
Cables and Pin Outs
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