Xi 8088

Introduction

Xi 8088 is an IBM PC/XT compatible processor board in ISA board form factor. It offers several enhancements over the standard IBM PC/XT, such as support of PS/2 keyboard and mouse and built-in real time clock with NVRAM (also known as CMOS setup memory).

Picture

Specifications

Processor: Intel 8088 or compatible, NEC V20.

Supports both standard 4.77MHz CPU clock and turbo, up to 13.33MHz CPU clock operation.

Coprocessor: Intel 8087.
RAM: Up to 832 KiB of usable system memory (640 KiB base memory, and up to 192 KiB UMB); Implemented using SRAM.
ROM: 128 KiB flash ROM. Configurable to either 64 KiB or 128 KiB.
8-bit ISA interface with several ISA/AT signals
PS/2 compatible keyboard and mouse controller
One 8237 direct memory access controller (DMAC)
Two 8259 programmable interrupt controllers (PICs), supporting the total of 15 interrupts; 10 interrupts available for extension cards
One 8254 programmable interval timer (PIT)
One DS12885/DS12887 real time clock and non-volatile RAM (RTC/NVRAM)

Firmware / BIOS (files are at the bottom of this page)

bios-0.9.0.tar.gz - Use bios128k-2.0.bin for programming new flash ROMs; use bios.bin with xiflash utility. Please refer to README.txt for more information about the BIOS.

xiflash-0.1.tar.gz - In system flash programming utility.

Hardware Documentation (files are at the bottom of this page)

Schematic

8088-SBC - Schematic - Color - 2.0.pdf

PCB Layout

8088-SBC - Board - Color - 2.0.pdf

Memory Map

Start Address	End Address	Size	Purpose	Comments
0000h	9FFFFh	640 KiB	Base memory
0A0000h	0BFFFFh	128 KiB	Display memory	Actual addresses and size might vary depending on the type of the video adapter
0C0000h	0EFFFFh	192 KiB	Upper memory blocks (UMB) and BIOS extension ROMs	Consists of six 32 KiB user configurable blocks, can be either mapped to SRAM (to be used as UMB) or used for BIOS extension ROMs
0E0000h	0EFFFFh	64 KiB	On-board BIOS extension ROM	System flash ROM can be mapped here, so it can be used for BIOS extensions
0F0000h	0FFFFFh	64 KiB	System BIOS	Currently BIOS uses only top 32 KiB of this space (0F8000h - 0FFFFFh). The other 32 KiB part is mapped to the flash ROM and can be used for BIOS extensions

I/O Ports Map

Port Address	Device and/or Function	Write	Read
00h	DMAC - Channel 0	Base/current address	Current address
01h	DMAC - Channel 0	Base/current word count	Current word count
02h	DMAC - Channel 1	Base/current address	Current address
03h	DMAC - Channel 1	Base/current word count	Current word count
04h	DMAC - Channel 2	Base/current address	Current address
05h	DMAC - Channel 2	Base/current word count	Current word count
06h	DMAC - Channel 3	Base/current address	Current address
07h	DMAC - Channel 3	Base/current word count	Current word count
08h	DMAC - Command/Status Register	Write command register	Read status register
09h	DMAC - Request Register	Write request register	N/A
0Ah	DMAC - Single mask register bit	Write single mask register bit	N/A
0Bh	DMAC - More register	Write mode register	N/A
0Ch	DMAC - Clear byte pointer flip-flop	Clear byte pointer flip-flop	N/A
0Dh	DMAC - Master clear/Read temporary register	Master clear	Read temporary register
0Eh	DMAC - Clear mask register	Clear mask register	N/A
0Fh	DMAC - Write all mask register bits	Write all mask register bits	N/A
10h-1Fh	Alias for 00h-0Fh (DMAC)
20h	Master PIC
21h	Master PIC
22h-3Fh	Aliases for 20h-21h (Master PIC)
40h	PIT - Channel 0
41h	PIT- Channel 1
42h	PIT- Channel 2
43h	PIT - Control Word
44h-5Fh	Aliases for 40h-43h (PIT)
60h	Keyboard controller
61h	Port B - Bit 0	0 = Disable PIT Channel 2 1 = Enable PIT Channel 2 (Note: Channel 2 is connected to the speaker)	0 = PIT Channel 2 disabled 1 = PIT Channel 2 enabled
	Port B - Bit 1	0 = Disable speaker 1 = Enable speaker	0 = Speaker disabled 1 = Speaker enabled
	Port B - Bit 2	0 = Disable turbo mode 1 = Enable turbo mode	0 = Turbo mode disabled 1 = Turbo mode enabled
	Port B - Bit 3	0 = Disable I/O check NMI 1 = Enable I/O check NMI (Note: Write 0 followed by 1 to clear the I/O check NMI state condition)	0 = I/O check NMI disabled 1 = I/O check NMI disabled
	Port B - Bit 4	N/A	PIT Channel 0 output divided by 2 (Toggles every 15 µs)
	Port B - Bit 5	N/A	PIT Channel 2 output
	Port B - Bit 6	N/A	0 = No NMI from I/O check 1 = NMI from I/O check
	Port B - Bit 7	N./A	Always reads as 0
62h-63h	Aliases for 60h-61h
64h	Keyboard controller
65h-6Fh	Aliases for 60h-04h
70h	RTC/NVRAM address, NMI control
71h	RTC/NVRAM data
72h-7Fh	Aliases for 70h-71h (RTC)
80h	DMA Page Register - Channel 1, POST register
81h	DMA Page Register - Channel 1
82h	DMA Page Register - Channel 1
83h	Unused
84h-9Fh	Aliases to 80h-83h
0A0h	Slave PIC
0A1h	Slave PIC
0A2h-0BFh	Aliases to 0A0h-0A1h
0C0h-0FFh	Unused, reserved
0100h-03FFh	Available for extension cards

Hardware Interrupts

Interrupt Number (IRQ#)	Default Software Interrupt Number	Device	Comment
0	08h	PIT - Channel 0	Default Frequency is 18.2 Hz
1	09h	KBC - Keyboard
2	0Ah	Cascade to Slave PIC
3	0Bh	Available
4	0Ch	Available
5	0Dh	Available
6	0Eh	Available
7	0Fh	Available
8	70h	RTC
9	71h	Available	BIOS redirects IRQ9 to IRQ2 vector
10	72h	Available
11	73h	Available
12	74h	KBC - PS/2 Mouse, or Available	Can be configured using jumper J3
13	75h	Math coprocessor exception	BIOS redirects IRQ13 to NMI vector
14	76h	Available
15	77h	Available

Jumpers, Connectors, and Switches

P1 - PS/2 Keyboard

Pin	Description
1	Keyboard data
2	Unused
3	GND
4	+5V
5	Keyboard clock
6	Unused

P2 - PS/2 Mouse

Pin	Description
1	Mouse data
2	Unused
3	GND
4	+5V
5	Mouse clock
6	Unused

P3 - Speaker

Pin	Description
1	Speaker output
2	Internal Speaker input *
3	Ground
4	+5V

*Note: To enable internal speaker connect a jumper across pins 1-2

P4 - Power LED

Pin	Description
1	LED's anode (+)
2	LED's cathode (-)

P5 - Turbo LED

Pin	Description
1	LED's anode (+)
2	LED's cathode (-)

J1 - Reset Switch

Pin	Description
1	Ground
2	Reset input

J2 - Turbo Switch

Position	Description
none	Turbo off
1-2	Turbo on
2-3*	Turbo is software controlled (Port 61h bit 2)

* Default setting

J3 - IRQ12

Position	Description
1-2*	IRQ12 is PS/2 mouse interrupt - connected to the keyboard controller
2-3*	IRQ12 is connected to the ISA bus

* Default setting

J4 - Enable ISA16 signals

Position	Description
1-2	/MEMW is connected to ISA C10 (/MEMW)
3-4	/MEMR is connected to ISA C9 (/MEMR)
5-6	LA17 is connected to ISA C8 (LA17)
7-8	LA18 is connected to ISA C7 (LA18)
9-10	LA19 is connected to ISA C6 (LA19)
11-12	ISA C2 - C5 (LA20 - LA23) are connected to ground

Note: Set all jumpers for Cirrus Logic GD542x VGA cards, remove for all other cards.

J5 - Clear NVRAM

Position	Description
none*	Normal operation
1-2	Clear NVRAM (CMOS setup memory)

* Default setting

SW1 - Reset Switch

Press SW1 to reset the system

SW2 - Memory Configurations Switch

Position	Description
1	ON = Map 0C0000h-0C7FFFFh to RAM
2	ON = Map 0C8000h-0CFFFFFh to RAM
3	ON = Map 0D0000h-0D7FFFFh to RAM
4	ON = Map 0D8000h-0DFFFFFh to RAM
5	ON = Map 0E0000h-0E7FFFFh to RAM
6	ON = Map 0E0000h-0EFFFFFh to RAM
7	ON = 64 KiB ROM starting from 0F0000h OFF = 128 KiB ROM starting from 0E0000h
8	ON = Monochrome display (MDA) OFF = Color display (CGA)

Notes:

SW2.7 must be ON if SW2.5 or SW2.6 are ON
VGA BIOS is usually mapped to 0C0000h-0C7FFFFh, when using VGA SW2.1 must be OFF

SW3 - I/O Wait States Configuration Switch

Position	Description
1*	ON = 1 I/O wait state
2	ON = 2 I/O wait states
3	ON = 3 I/O wait states
4	ON = 4 I/O wait states

* Default

Note: One and only one of SW3 switches must be on

Bill of Materials (BOM)

BOM Notes

BOM

Component type	Reference	Description	Quantity	Possible sources and notes
PCB		Xi 8088 PCB Version 2.0	1	Order from Sergey
Battery Holder	BT1	CR2032 batter holder, 20 mm lead spacing	1	Jameco 355434, Mouser 122-2620-GR, 122-2520-GR, 122-2420-GR, Radio Shack 270-009
Capacitor	C1 - C46	0.1 uF ceramic, 5.08 mm lead spacing	46	Mouser 810-FK28X7R1H104K, 80-C323C104K5R Jameco 25523
Capacitor	C47 - C51	10 uF ceramic, 5.08 mm lead spacing	5	Mouser 810-FK24X5R1C106K Note: Can be replaced with tantalum or electrolytic capacitors
Capacitor	C52, C53	33 pF ceramic, 5.08 mm lead spacing	2	Mouser 80-CK05BX330K-TR Jameco 1947010 Note: Install only if using CMOS type of U1 82C84, for NMOS 8284 install R8 and R9 instead
Capacitor	C54	5-30 pF trimmer capacitor	1	Mouser 81-TZ03R300F169B00 Jameco 136979
Capacitor	C55-C58	47 pF ceramic, 5.08 mm lead spacing	4	Mouser 80-CK05BX470K-TR Jameco 1947036
Capacitor	C59	0.01 uF ceramic, 5.08 mm lead spacing	1	Mouser 80-C322C103K1R5CA Jameco 597281
Diode	D1	1N4148	1	Jameco 36038, 179215; Mouser 512-1N4148, 771-1N4148-T/R
Diode	D2, D3	Bi-level LED indicator	1	Mouser 696-SSF-LXH240GYD Jameco: Search for "Bi-Level LED", choose one with pins in square pattern (not in line)
Fuse	F1	1.1A polyfuse, 5.04 mm lead spacing	1	Mouser 576-16R110BPR Jameco 199912
Connector	J1, J2, P3, P4, P5	13x1 pin header	1	Mouser 649-68000-113HLF
Connector	J3	3x1 pin header	1	Jameco 109576; Mouser 649-69190-103HLF, 649-78229-103HLF
Connector	J4	6x2 pin header	1	Mouser 649-68021-212HLF
Connector	J5	2x1 pin header	1	Jameco 108338; Mouser 649-78229-102HLF
Connector	P1	6 pin Mini-DIN connector (Purple)	1	Mouser 806-KMDGX-6S-BS2715C (Purple) Jameco 119475 (Black)
Connector	P2	6 pin Mini-DIN connector (Green)	1	Mouser 806-KMDGX-6S-BS3395C (Green) Jameco 119475 (Black)
Transistor	Q1	PN2222A	1	Mouser 512-PN2222ATA
Resistor	R1	100 kOhm, 1/4 W	1	Mouser 291-100K-RC
Resistor	R2, R4, R5	470 Ohm, 1/4 W	3	Jameco 690785 Mouser 291-470-RC
Resistor	R3	10 kOhm, 1/4 W	1	Jameco 691104 Mouser 291-10K-RC
Resistor	R6	1 kOhm, 1/4 W	1	Mouser 291-1K-RC
Resistor	R7	33 Ohm, 1/4 W	1	Mouser 291-33-RC
Resistor	R8, R9	510 Ohm, 1/4 W	2	Mouser 291-510-RC Note: Install only if using NMOS type of U1 8284, for CMOS 82C84 install C52 and C53 instead
Resistor Array	RR1 - RR3	10 kOhm, 10 pin, bussed resistor array	3	Mouser 266-10K-RC
Resistor Array	RR4, RR5	10 kOhm, 6 pin, bussed resistor array	2	Mouser 264-10K-RC
Resistor Array	RR6	470 Ohm, 6 pin, bussed resistor array	1	Mouser 264-470-RC
Speaker	SP1	12 mm speaker	1	Mouser 665-AT-1224TWTR
Switch	SW1	6 mm tactile switch, right angle	1	Mouser 653-B3F-3152,
Switch	SW2	8 positions DIP switch	1	Mouser 571-54356405
Switch	SW3	4 positions DIP switch	1	Mouser 506-54356402
IC	U1	8284 or 82C84 clock generator	1	Avnet Express Intersil CP82C84AZ Unicron Electronics (82C84)
IC	U2	8088, 80C88, NEC V20, or NEC V20HL CPU	1	Jameco 34358 (NEC V20, 8 Mhz), 52169 (8088, 8 MHz), 52142 (8088, 5 MHz) Unicorn Electronics Avnet Express Intersil IP80C88 Utsource, eBay
IC	U3	8087 FPU	1	8087 FPU is an optional part Unicorn Electronics, Utsource, eBay
IC	U4	8288 or 82C88 bus controller	1	Avnet Express Intersil CP82C88Z Unicorn Electronics 82C88 Note: AMD 8288 part is not recommended
IC	U5, U6	8259 or 82C59 PIC	2	Avnet Express Intersil CP82C59A-12Z Jameco 52775 Unicorn Electronics 82C59 or 8259
IC	U7	8237 or 82C37 DMAC	1	Unicorn Electronics 82C37 or 8237 eBay
IC	U8	8254 or 82C54 PIT	1	Mouser 968-CP82C54-10Z Avnet Express CP82C54 Jameco 52716, 52708 Unicorn Electronics 82C54 or 8254
IC	U9	8242, 82C42, VT82C42N, HT6542B	1	Note: Original 8242 and 82C42 chips (usually made by Intel, Mitsubishi, or NEC) are generic mircocontrollers. Make sure to get one with PS/2 keyboard controller firmware, or use a dedicated keyboard controller, such as VIA VT82C42N (recommended).
IC	U10	DS12885 or DS12887	1	Mouser 700-DS12885N Mouser 700-DS12887A Avnet Express DS12885N+ Avnet Express DS12887A+ Jameco 1194513, 1194492 (DS12885) Jameco 133452 (DS12887) Note: DS12887 has a built-in battery and 32768 Hz crystal, no need to install BT1 and X2
IC	U11, U12	512 KiB SRAM, 32 pin DIP - AS6C4008-55PCN	2	Mouser 913-AS6C4008-55PCN Jameco 1927617
IC	U13	128 KiB flash, 32 pin DIP - 39SF010, 29F010, 29C010	1	Mouser 804-39SF010A7CPHE, 804-GLS29EE010-70PHE Jameco 242608, 242595, 242587
IC	U14	74LS670 or 74HCT670	1	Mouser 595-SN74LS670N, 771-HCT670N652 Unicorn Electronics 74LS670
IC	U15 - U17	74F573 or 74ACT573	3	Mouser 595-SN74F573NE4, 595-SN74F573N, 595-SN74ACT573N, 595-CD74ACT573E Jameco 282642 Unicorn Electronics 74F573
IC	U18 - U21	74F245 or 74ACT245	4	Mouser 595-SN74F245N, 771-NF245N602, 595-SN74ACT245N, 595-CD74ACT245E Jameco 287144 Unicorn Electronics 74F245
IC	U22, U23	74F244 or 74ACT244	2	Mouser 595-SN74F244N, 771-NF244N602, 595-SN74ACT244N, 595-CD74ACT244E, 863-MC74ACT244NG Jameco 212054 Unicorn Electronics 74F244
IC	U24 - U26	74ALS175, 74AHCT175, or 74ACT175	3	Mouser 595-SN74ALS175NE4, 595-SN74ALS175N, 595-CD74ACT175E Unicorn Electronics 74ALS175, 74AHCT175
IC	U27, U28	74ALS139 or 74AHCT139	2	Mouser 595-SN74ALS139N, 595-SN74AHCT139N Jameco 46623, 301268, 63773, 239011 Unicorn Electronics 74ALS139
IC	U29	74ALS138 or 74AHCT138	1	Mouser 595-SN74ALS138AN, 512-DM74ALS138N, 595-SN74AHCT138N Jameco 46607, 46608, 301233, 44927 Unicorn Electronics 74ALS138, 74AHCT138
IC	U30	74LS92	1	Mouser 595-SN74LS92NE4 Jameco 48143 Unicorn Electronics 74LS92
IC	U31 - U33	74ALS74 or 74AHCT74	3	Mouser 595-SN74ALS74AN, 512-DM74ALS74AN, 595-SN74AHCT74N Unicorn Electronics 74ALS74, 74AHCT74
IC	U34, U35	74ALS32 or 74AHCT32	2	Mouser 595-SN74ALS32N, 512-DM74ALS32N, 595-SN74AHCT32N Jameco 44134, 47466, 47467, 295515 Unicorn Electronics 74ALS32, 74AHCT32
IC	U36	74ALS20 or 74ACT20	1	Mouser 595-SN74ALS20ANE4, 595-SN74ALS20AN, 595-CD74ACT20EE4, 595-CD74ACT20E Unicorn Electronics 74ALS20
IC	U37	74ALS11, 74AHCT11, or 74ACT11	1	Mouser 595-SN74ALS11AN, 595-SN74ACT11N Unicorn Electronics 74ALS11
IC	U38	74LS06	1	Mouser 595-SN74LS06N Jameco 46359 Unicorn Electronics 74LS06
IC	U39	74F04, 74ACT04	1	Mouser 595-SN74F04N, 595-SN74ACT04N Note: This IC should have higher output current (about 20 mA), 74LS04, 74ALS04, or 74AHCT04 can be used, but it might result in stability issues especially on higher CPU frequency.
IC	U40	74ALS04, 74AHCT04	1	Mouser 595-SN74ALS04BNE4, 595-SN74ALS04BN, 595-SN74AHCT04NE4 Jameco 970621 Unicorn Electronics 74ALS04, 74AHCT04
IC	U41, U42	74ALS02, 74AHCT02	2	Mouser 595-SN74ALS02ANE4, 595-SN74ALS02AN, 595-SN74AHCT02N Unicorn Electronics 74ALS02, 74AHCT02
IC	U43 - U45	74ALS00, 74AHCT00	3	Mouser 595-SN74ALS00AN, 595-SN74AHCT00NE4, 595-SN74AHCT00N Jameco 245294 Unicorn Electronics 74ALS00, 74AHCT00
Crystal Oscillator	U46	Turbo clock oscillator 24 MHz	1	Note: U46 frequency should be desired CPU turbo frequency multiplied by 3 (24 MHz for 8 MHz CPU, 30 MHz for 10 MHz CPU, etc. Mouser 774-MXO45-3C-24.0 (24 MHz) Jameco 2135321 (24 MHz), 325438 (30 MHz)
IC Socket	U2, U3, U7, U9	40 pin 600 mil DIP socket	4	Mouser 517-4840-6000-CP, 649-DILB40P223TLF Jameco 41111
IC Socket	U11 - U13	32 pin 600 mil DIP socket	3	Mouser 517-4832-6000-CP, 649-DILB32P223TL Jameco 112301
IC Socket	U5, U6	28 pin 600 mil DIP socket	2	Mouser 517-4828-6000-CP, 649-DILB28P223TLF
IC Socket	U8, U10	24 pin 600 mil DIP socket	2	Mouser 517-4824-6000-CP
IC Socket	U4, U15 - U23	20 pin 300 mil DIP socket	10	Mouser 517-4820-3000-CP, 649-DILB20P-223TLF Jameco 112248
IC Socket	U1	18 pin 300 mil DIP socket	1	Mouser 517-4818-3000-CP
IC Socket	U14, U24 - U29	16 pin 300 mil DIP socket	7	Mouser 517-4816-3000-CP, 649-DILB16P-223TLF Jameco 37373
IC Socket	U30 - U45	14 pin 300 mil DIP socket	16	Jameco 37162 Mouser 517-4814-3000-CP, 649-DILB14P-223TLF
Oscillator Socket	U46	4 pin 300 mil DIP full can oscillator socket	1	Mouser 535-1107741 Jameco 133006
Crystal	X1	14.31818 MHz AT cut crystal	1	Mouser 73-XT49S1431-20
Crystal	X2	32768 Hz tune fork crystal	1	Mouser 732-C002RX32.76K-EPB, 695-CFS206-327KB-U Jameco 14584
ISA Mounting Bracket		Keystone 9205	1	Mouser 534-9205 Need to drill holes for PS/2 connectors, LEDs and the reset switch
Screw	HOLE1, HOLE2	Screw 4-40 diameter, 1/4" length	1	Mouser 534-9900

Replacement Notes

Intel 8xxx ICs - Either CMOS (8xCxx) or NMOS/TTL ICs can be used. CMOS and particularly NEC V20 CPU and Intersil 82Cxx peripheral ICs are preferred because of their lower power consumption and higher performance
74xx logic ICs - Advanced TTL-LS (74ALS, 74F) or advanced TTL compatible CMOS (74AHCT, 74ACT) are recommended, especially for turbo CPU clock frequencies. Some parts (74LS92, 74LS06, 74LS670) are not available in these series, so regular 74LS and 74HCT should be used. With that being said most of logic parts are not very speed sensitive, especially if running on standard 4.77 MHz clock, with exception of 74ALS74 in wait state generator, so generally 74LS series ICs can be used. 74F and 74ACT are preferred parts for bus driving circuits (74x244, 74x245, 74x573)
For higher clock frequency (more than 8 MHz) along with 74ALS or 74AHCT for most logic, it is recommended to use faster U31, U32, U24 and U25. For example 74F or 74ACT series.