IBM PC/XT Hardware Data

I/O Address Map
8088 Hardware Interrupt Listing
8255A I/O Bit Map

System Memory Map

I/O Address Map

Address (HEX)	Usage
000-00F	DMA Chip 8237A-5
020-021	Interrupt 8259A
040-043	Timer 8253-5
060-063	PPI 8255A-5
080-083	DMA Page Register
0AX*	NMI Mask Register
0CX	Reserved
0EX	Reserved
200-20F	Game Control
210-217	Expansion Unit
220-24F	Reserved
278-27F	Reserved
2F0-2FF	Reserved
2F8-2FF	Asynchronous Communications(Secondary)
300-31F	Prototype Card
320-32F	Fixed Disk
378-37F	Parallel Printer
380-38F	SDLC Communications
3A0-3AF	Reserved
3B0-3BF	IBM Monochrome Display/Printer
3C0-3CF	Reserved
3D0-3DF	Color/Graphics
3E0-3E7	Reserved
3F0-3F7	Diskette
3F8-3FF	Asynchronous Communications(Primary)

* At power-on time, the Non Maskable Interrupt(NMI) into the 8088 is masked off. This mask bit can be set and reset via system software as follow

Set mask: write 80H to I/O Address 0A0H (enable NMI) Clear mask: write 00H to I/O Address 0A0H (disable NMI)

8088 Hardware Interrupt Listing

Number	Usage
NMI	Parity
0	Timer
1	Keyboard
2	Reserved
3	Asynchronous CommunicationsSDLC Communications(Secondary)
4	Asynchronous Communications(Primary) Communications
5	Fixed Disk
6	Diskette
7	Parallel Printer

8255A I/O Bit Map

Port No. Type BiT(HEX)

usage

		PA0	+Keyboard Scan Code	0	or	Diagnostic Outputs	0
		PA1		1			1
		PA2		2			2
060	I	PA3		3			3
		PA4		4			4
		PA5		5			5
		PA6		6			6
		PA7		7			7
		PB0	+Timer 2 Gate Speaker
		PB1	+Speaker Data
		PB2	Spare
061	O	PB3	Read High Switches or Read Low Switches
		PB4	-Enable RAM Parity Check
		PB5	-Enable I/O Channel Check
		PB6	-Hold Keyboard Clock Low
		PB7	-(Enable Keyboard) or (Clear Keyboard)
.	.	PC0	Loop on Post	Sw-1	or	Display 0	**Sw-5
		PC1	+Co-Processor Install	Sw-2	or	Display 1	**Sw-6
		PC2	+Planar RAM Size 0	*Sw-3	or	#5-1/4 Drives 0	***Sw-7
062	I	PC3	+Planar RAM Size 1	*Sw-4	or	#5-1/4 Drives10	***Sw-8
		PC4	Spare
		PC5	+Timer Channel 2 Out
		PC6	+I/O Channel Check
		PC7	+RAM Parity Check
063			Command/Mode Register
Mode	Register	Bit	:7 6 5 4-3 2 1 0
Value	(Binary)		: 1 0 0 1-1 0 0 1
Value	(HEX)		: 9 9

*	Sw-4	Sw-3	Amonut of Memory on System Board
	0	0	64K
	0	1	128K
	1	0	192K
	1	1	256K
**	Sw-6	Sw-5	Display at Power-Up Mode
	0	0	Reserved
	0	1	Color 40 X 25 (BW Mode)
	1	0	Color 80 X 25 (BW Mode)
	1	1	IBM Monochrome 80 X 25
***	Sw-8	Sw-7	Number of 5-1/4 inches Drive in System
	0	0	1
	0	1	2
	1	0	3
	1	1	4

Note: I = Input, O=Output
A plus(+) indicates a bit value of 1 performs the specified function.
A minus(-) indicates a bit value of 1 performs the specified function.
PA Bit=0 implies switch "ON". PA Bit=1 implies switch"OFF".

System Memory Map

Address (HEX)	Usage
00000 3CFFF	256K R/W Memory on System Board
40000 9FFFF	256K R/W Memory Expansion in I/O Channel
A0000 AFFFF	128K Reserved
B0000 B3FFF	Monochrome Display Adaptor
B4000 B7FFF	.
B8000 BBFFF	color Graphic Display Adaptor
BC000 BFFFF	.
C0000 C7FFF	192K Read Only Memory Expansion and Control
C8000 CBFFF	Fixed Disk Controller
CC000 EFFFF	.
F0000 FFFFF	64K Base System ROM BIOS and BASIC Interpreter