Mark's Ohio Scientific (OSI) Board Catalog

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Last update Sep-18-2011

Hardware Index by board number.

Picture Description
OSI300 CPU OSI300 6502 CPU

(Image courtesy of

Model 300 Trainer ~1976

Single board trainer computer. Using 6502 CPU and 6810 128x8 Static RAM. There are switches and indicators for 8 data lines and 7 address lines, as well as swiches for RUN, RESET, LOAD, NMI and ROM.


OSI400 CPU OSI400 6502 or 6800 CPU

(Image courtesy
Model 400 CPU

Supports one of 6502, 6502A, 6501, 6512, Motorola 6800, 6800A, 6802, 6802B PROM supports up to two of the following: OSI 65A Serial Monitor, OSI 65V Video Monitor, OSI 65F Floppy disk bootstrap RAM: optional 1Kx8 of 2102 Serial: ACIA based 20ma current loop or RS-232, up to 100,000 baud. Parallel: Supports one of the following PIA devices for up to 16 I/O lines: 6820, 6520, 6522, 6530, 6830 Buffering for up to 250 OSI boards. Provisions for user supplied front panel and DMA capability Addressing for 2 PROMS: $FExx, $FFxx RAM: $0000- $03FF PIA: $FDxx ACIA $FCxx

OSI400 schematics

OSI420 4Kx8(12) RAM OSI420 4K Static RAM Model 420 4Kx8/4Kx12 static RAM memory board

Uses 2102 1Kx1 static memories, with optional battery backup using 2 on-board NiCd cells or external battery. It has 18 address bits allowing for 256K of memory in a system. It can be populated as 4Kx12 for use with the 560Z PDP-8. Address: any 4K memory address $0000-$0FFF

OSI420C schematics
OSI420C manual   (courtesy of Bill Dromgoole)

OSI board OSI430 Cassette & Analog I/O

OSI board OSI430B Cassette & Analog I/O

(Image courtesy of Bill Dromgoole)

Model 430 / Model 430B © 1977 Cassette & Analog I/O

Can be populated for Kansas City Standard Cassette Interface or for RS-232.
Cassette 300 to 1200 baud, RS-232 or current loop max 50K baud.
Has 8 parallel I/O lines, 2 fast D/A converters, and fast tracking A/D converter with 8 channel multiplexer. 

Uses S1883 UART for serial I/O
D/A - two 8bit 2v output 300ns settling time MC1408L8 chip
A/D - 8bit -1 to +1v one conversion per system cycle, usable with signals up to 20 KHz bandwidth. 1408L8 8-channel multiplexor National 3705
8 parallel I/O - 8 TTL latched outputs, 3 used by multiplexor,
8 TTL inputs, non-latched

Normally located @ $FB0x. Decodes 3 lowest adddress bits

$FB00 D/A #1 out A/D conversion
$FB01 D/A #2 out User 8bit in
$FB02 User 8bit out  
$FB03   UART (-RDE)
$FB04 UART (-TDS)  
$FB07 UART (-RDA)  

OSI430B schematics
OSI430B manual  (courtesy of Bill Dromgoole)
OSI 440 Video board OSI440 Video board

(Image Courtesy Bill Dromgoole)

Model 440B Video board

The OSI 440 video graphics board is a versitile high performance computer to TV interface. It can be economically populated as a terminal providing up to 32x32 characters on a screen and a keyboard input port. It can maximally be populated for 32x32 characters, 128x128 graphics and 4 color alphabetics.

Video: - 2V p-p into hi-Z, composite or ttl sync 60hz, 15.450Khz
Font: 5x7 uppercase ASCII
Format: 32 rows x 32 columns, unmodified TV sets typically display 24 x 24.
Keyboard input: 7 bit parallel ASCII with continuous strobe of at least 50us long-pulsed strobe
RAM: 1K x 6bit default
Graphics option: requires 446 kit, 420 memory board, (additional parts)
Address: Normally jumpered for $D000
Color output: uses upper 2 bits of character to select character color. white=0, red=1,green=2,yellow=3

OSI440B schematics
OSI440B manual  (courtesy of Bill Dromgoole)

OSI board OSI450B & 455 Eprom Boards

(Image courtesy
Model 450B 8K Eprom & Parallel I/O + prom programmer
Model 455 4K Eprom & Parallel I/O © 1977

These boards provide EPROM storage and up to 16 lines of parallel I/O. (req +5, -9v) Full address decoding anywhere in 64K address space. 4K or 8K
Uses 6820 PIA at $xFxx
455 Board: up to 16 1702 type PROMS (4K max)
450 board : up to 16 6823 type PROMS (8K max), includes onboard EPROM programmer (req -50v programming voltage)

OSI450B schematics

OSI board OSI460Z 3 CPU Expander

(Image Courtesy Bill Dromgoole)
Model 460Z CPU Expander

The 460Z 3 CPU Expander board comes ready to accommodate a Z-80 and 6100 CPU as well as one of a Signetics 2650, Fairchild F8, or RCA COSMAC 1802. In additon to the 3 processors it accommodates 4 PIAs for control plus several multiplexers and demultiplexers. The 3 CPU expander runs downstream of the 6502 host. The 6502 executive has full line-by-line control of the 460Z and can reach the bus through a 4K mapped "porthole". It can run the 460Z CPUs at full speed or in a step at a time, monitor at full speed, "trap" certain instructions, start and stop the host processor, permit "general" memory access and in every way permit full multiprocessor operation.
OSI470 Floppy Disk Controller OSI470 Floppy Disk Controller

Model 470 disk controller board(same as Model 471)
Uses 6850 ACIA & 6520 PIA
Can optionally be configured as printer parallel I/O card

PIA: *=output
*PB7 - Head Load *PA7 - Index
 PB6 - Low Current  PA6 - Select Drive 2
*PB5 - Select Drive 1  PA5 - Write Protect (optional)
 PB4 - Fault Reset  PA4 - Ready (Drive 2)
*PB3 - STEP  PA3 - Sector (optional)
*PB3 - STEP  PA3 - Sector (optional)
*PB2 - Step In  PA2 - Fault
 PB1 - Erase Enable *PA1 - Track 0
*PB0 - Write Enable *PA0 - Ready (Drive 1)
*PB3 - STEP  PA3 - Sector (optional)

ACIA: DCD wired to -(-Index & -Sector)
TXclk: 250KHz = 8", 125KHz = 5.25"

OSI470 floppy schematics   OSI470 printer I/O schematics

OSI board OSI480 Backplane

(Image courtesy of Bill Dromgoole)
Model 480 Backplane

8-slots with buffering allowing additional 480 boards to be connected together for up to 250 slots

OSI480 manual  (courtesy of Bill Dromgoole)

OSI board OSI495 Prototyping Model 495 Prototyping board

Supports up to 40 16-pin package chips & 8 40 pin chips
OSI498 Card Extender OSI498 Card Extender

(Image courtesy
Model 498 Card Extender

Used to extend a card out of the cage for easy servicing. Has connectors on the top to service Challenger system boards, and along the edge for some OSI 400 configurations.
(Image courtesy of Bill Degnan)

Model 500 CPU © 1977, update © 1978, and the revised Model 500B CPU © 1978
6502 CPU board with 4 2Kx8 ROMs supplied with Microsoft Basic in ROM, 4K of on-board RAM, RS-232 or current loop, ACIA, PIA, 3 256x8 system ROM pages. Can be used as the controller for 560Z. Can be used with 430B audio cassette interface, 440B video graphics board, & floppy disk system. (There are at least two versions of the original 500 board, plus a 500B board that has a single EPROM socket, replacing the three 256byte 1702 EPROMS.)
Item Address
RAM $0000-$0400 (4Kx8 using 16 2102 static RAM chips)
ROM (4) 2Kx8 $A000-BFFF (2316)
System ROM (3)
(1 on RevB):
$FDxx, $FExx, $FFxx (1702)
Rev B board uses single 2K? ROM
6850 ACIA $FCxx
6820 PIA $F7xx

Works with OSI 65A serial PROM monitor, 65V video PROM monitor, and floppy disk bootstrap PROMs
Used in OSI C2P systems with OSI540A monochrome graphics adapter.

OSI500 schematics 

OSI 502 CPU board OSI502 CPU Board Model 502 CPU board © 1978

CPU board w/ ROM, ACIA 8K Basic in ROM via 4 2Kx8 ROMS, 2K Monitor ROM, 8K RAM
Item Address
RAM $0000-$1FFF (8Kx8 using 2114 static RAM chips)
ROM (4) 2Kx8 $A000-BFFF (2316)
System ROM (1)2Kx8 $FDxx, $FExx, $FFxx (uses priority encoder to map various pages of ROM to these pages)
6850 ACIA $FCxx with built in KCS Cassette interface

Used in OSI C4P and C8P systems
(This 502 board has the C2E ROM Monitor mods which map a 2K EPROM into $F800-$FFFF except for serial I/O at $FC00.)

OSI502 schematics

OSI 505 CPU board OSI505 CPU + Disk Ctrl

OSI 505B CPU board OSI505B CPU + Disk + I/O
Model 505 & Model 505B CPU & Floppy Interface Board © 1979

CPU board w/ ROM, ACIA, Floppy Disk I/O, Real Time Clock
Item Address
System ROM (1)2Kx8 $FDxx, $FExx, $FFxx
(uses priority encoder to map various pages of ROM to these pages)
6850 ACIA for serial I/O $FCxx
(Baud jumpers for 75,150,300,600,1200,2400,4800,9600)
6850 ACIA for disk I/O $C01x
6820 PIA for I/O $F70x-F703
CA2 can be wired to WAIT input allowing control of CPU speed, 1or 2Mhz
CB2 output controls CTS select from Modem or Printer serial interface
6820 PIA for disk I/O $C00x CB1 connected to 400mSEC (2.5/sec) clock divided from system clock (RTC)

505B has I/O at $C704-C70E for connection to A15 I/O board which contains connectors for keypads, joystick, buffered I/O contains A0-A3, 2, R/W, D0-D7 for Head End Cards. (MDS-since it requires external hardware, without hardware installed, looks like NULLREAD space I think...)
Uses disk I/O connector board A-13
Case uses port I/O connector board A-15
505B Used in OSI C4PMF systems

OSI505B schematics

OSI 510 CPU board OSI510 3 CPU Board

Model 510 Triple CPU Board (6502, Z80, 6800) © 1979

3 CPUs: 6502A, 6800, Z-80, ACIA, PIA, 3 1702A PROMS for 6502 (256x8), 1 1702A PROM for 6800
Address decoding for up to 1MB memory
6502 Proms at $FDxx, $FExx, $FFxx
6800 Prom at $FFxx
Processor selection manual or connected to PIA PA6, PA7 (01 = Z80, 10=6800, 11=6502)
PIA PA0-PA3 -> A16 -A19.PA4 ->ROM/RAM sel, PA5->Processor Switch
Also configured as 2 CPU system board with 6502A & Z-80-4, 68B50, 6821, 6810 & 2716 DMon EPROM labeled OSI CP-1

OSI510 schematics

OSI520 16K RAM board OSI520B
OSI520 16K RAM board OSI520C 16K RAM Board

Model 520 RevB 16K RAM board © 1977
Model 520 RevC 16K RAM board © 1980

Uses 32 4Kx1 EMM 4200 /GTE 4300 22-pin static RAMs (3 voltages, +5, +12, -9) fully populated to 16K RAM

OSI520 schematics

OSI board OSI522 48K RAM Board Model 522 48K RAM board © 1981

Uses 48 1Kx8 22 pin DIP RAM chips (GTE 8104/ NEC D421D) fully populated to 48K RAM
OSI board OSI524 64K RAM Board Model 524 64K Static RAM board © 1981

Uses up to 32 2Kx8 static RAM (NEC D4016D-1) but generally populated with 24 chips yielding 48K
OSI 525 Dual Port 16 K RAM board OSI525 16K Dual Port RAM Model 525 16K Dual Port RAM © 1981

Uses 4K, 8K, or 16K of 2114 1Kx4 static rams, configurable as single or dual port. Used in Hard Disk systems
OSI 527 Static RAM board OSI527 24K Static RAM Board Model 527 24K static RAM board © 1978

Usually populated as 8K, 16K, 24K board using 2114 static rams. Additional address decoding for up to 1MB (A6-A19). Used in OSI C4PMF

OSI527 schematics

OSI board OSI530 DRAM Board Model 530 Dynamic RAM Board

Can be populated for 16K, 32K or 48K using 4027 4kx1 16pin DRAM chips. Requires +5/+12/-9 Had address decoding for up to 20 bits.
OSI board OSI535 DRAM Board Model 535 4116 Dynamic RAM Board

Uses up to 24 4116 dynamic RAM chips for 48K of memory. Requires +5/+12/-5(-9v)
OSI board OSI538 Universal Memory Board Model 538 Universal Memory board © 1980

Contains 16 28pin dip sockets. May be populated with +5v only EPROM, ROM or static RAMs. Supports up to at least 8K EPROM.
OSI 540 mono video board OSI540A Video Board

(Image courtesy of Bill Degnan)

Model 540 Rev A video board © 1977

Supports 32x32, and 64x32 video modes B&W, with 542 polled keyboard interface socket Character memory $D000-D7FF each display row always $40 bytes long Can be populated with 6bit of memory for 64 uppercase characters, or 8bit for full OSI character set. Contains KCS cassette interface for serial <-> cassette conversion.

OSI540A and 542A schematics

OSI 540 video board OSI540B Video Board

Model 540B video board © 1978

Supports 32x32, and 64x32 video modes with color, 542 keyboard interface socket Character memory $D000-D7FF each display row always $40 bytes long Color memory $E000-E7FF 4bits.
bit 0: 0= normal(bright txt, color background), 1= inverse(dark txt, bright background)
bit 1-3: 0=yellow, red, green, olive, blue, purple, sky blue, black

Write Register @ $DE00 controls video modes:
bit 0 1=32, 0=64
bit 1 1=tone on (542 keyboard)
bit 2 1=color on
bit 3 1=enable 38-40Khz AC Home control output

Read Register @ $DE00
bit 7 = video timing counter bit, 0 for 1/120 second, 1 for 1/120 second, based on video clock (60Hz)

OSI540B schematics

OSI 542B polled keyboard OSI542B
Polled Keyboard + Sound

OSI 542C polled keyboard OSI542C Adds reset delay

Model 542 ©1977, Model 542B ©1978, and Model 542C ©1980 Polled Keyboards

Connects to 540A or 540B Video board via a 16-pin ribbon cable which plugs in to a socket on both ends.
Original Model 542 polled keyboard contains 8x8 keyboard matrix interface only. Model 542B adds tone, 8-bit resistor ladder DAC "noise" outputs, and an interface for the A15 board. The A15 board provides ports for joysticks or external number pads, in addition to other connectors.
An updated Model 542C incorporates a several second delay to the Break key before performing a system Reset.
Keyboard write @ $DF00 sets row, read at $DF00 reads columns. A bit is set when a key is pressed. (This is the opposite of the OSI600 C1/Superboard keyboard.)
The joystick buttons and keyboard keys are mapped as follows:

OSI polled keyboard matrix
Rd Col bit
Wr Row Sel


Tone enable when bit 1 (0x02) is set at $DE00
Tone generator: frequency out = 49152/I where I = value stored at $DF01(~192Hz - 49152hz)
DAC: Capacitively coupled output from an R2R resistor DAC of value stored @ $DF01
OSI542B schematics

OSI numeric keypad OSI543 Numeric Keypad Model 543 Numeric Keypad © 1980

Numeric Keypad accessory. Used with OSI542 polled keyboard
OSI 550 16 port serial board OSI550 Serial I/O Board Model 550 16 port 6850 Serial Port Board © 1977 (CA-10x)

Populated with up to 16 6850 ACIA. Typically used with multishare system and serial system (C3-series) although it can be used with any backplane based system.
Mapped $CF00-$CF1F (ACIA 0 to ACIA 7)
OSI 555 RAM I/O board OSI555 Multi I/O Board

Model 555 Multi I/O expansion & RAM © 1979

"Jungle Board" Contains up to five 6850 style ACIA and two 6821 PIA Has space for up to 8K of 2114 RAM Provides parallel & serial I/O capabilities for printers, timeshare terminals, console & network interface.

4K RAM $D000
4K RAM $E000
4 RS-232 port $CExx
1 network node interface
NEC compatible interface
Centronics compatible interface

OSI555 schematics

OSI 560Z CPU board OSI560Z CPU Board

(Image courtesy of Bill Dromgoole)

Model 560Z CPU expander © 1977

Supports Z80 CPU and IM-600 (PDP-8 compatible) microprocessors plus three-way bus switching and run/single step circuitry. The 560Z runs under the command of a 6502 based 400, 500, or 510 system. Can support 64K of memory & I/O, but occupies only 4K of 6502 memory through a "sliding port-hole"

OSI560Z schematics

OSI 567 board OSI567 Votrax Board Model 567 speech synthesizer board (CA-14) 1978?-1980?

OSI speech synthesis board using epoxied Votrax VSL module. The Votrax voice synthesizer module has the capability of generating English speech phonetically. The supporting software simply feeds the phoenetic spelling of English words to the module which generates medium quality spoken words. Generates all English phonemes and 4 levels of inflection. CA14 also includes voice recognition experimenters area with a five filter feature extractor with zero crossing detectors and envelope filters. CA-14 in conjunction with CA-22 high speed analog I/O module provides a complete voice recognition lab.
OSI 570 controller board OSI570 CA-12 controller board Model 570 controller board for CA-12 © 1980

Contains interface circuit for the 572 3 parallel I/O board, part of the CA-12 package.

OSI 570B 8port & clock board OSI570B I/O & Clock Board Model 570B Multiple Accessory Bus w/ 8 Port I/O & Real Time Clock (CA-20) © 1980

Contains National Semiconductor NS58167 real time clock chip, 6821 PIA, and battery holders for 3 AA size batteries. 8 16-pin DIP sockets for external interfacing Head End Cards. Needs 1 OSI slot in backplane. Recommended for C2 & C3 series computers, may also be made to work in C4P & C8P.

OSI570B schematics & Head End card overview

OSI 3 PIA remote board OSI572 PIA Remote Board Model 572 3 PIA expansion (CA-21) 1978

3 PIA (6821) expansion board with OSI 48-bus connectors can be used as head end card or on OSI 48 backplane. Also comes configured with prototyping area.
Included as part of CA-12 96 line parallel I/O which used 2 OSI572 boards with OSI570 controller board

OSI572 schematics

OSI EPROM programmer board OSI573 EPROM programmer Model 573 EPROM programmer (CA-23)

Head End Card EPROM Programmer for 1K to 8K EPROMS.

OSI573 schematics & manual

OSI Analog I/O Board OSI574 Analog I/O
** Large Image Needed!
Model 574 Analog I/O Board (CA-22) © 1980

Head End Card Analog I/O Board - Analog I/O Designed as a high speed analog I/O but differs from other head end cards in that it can be plugged directly into the computers standard bus. 16 channel analog multiplexor, sample & hold. 8 or 12 bit operation. 66K samples/sec 8bit 28K in 12bit. 2 high speed DAC, 8 or 12 bits. 3 TTL level inputs, 6 open collector outputs. Contains 2 Burr-Brown "ADC80AGZ-12" and 2 Burr-Brown "DAC80 Z-CBI-I" Factory configured for +/-10v.

OSI574 schematics OSI574 manual ADC80, DAC80, SHC298AM chips

OSI prototyping board OSI575 Prototyping Board Model 575 Prototyping board (CA-24)

Head End Card Prototyping board. Solderless breadboard design. Contains clock Generator 25K-70KHz, and 16 stage divider. Features PIA as well as provisons for direct user connection of devices such as 6850 ACIA. Also features 16 switches and 16 LEDs.

OSI575 schematics & experimenters manual

OSI 580 board OSI580 Board Model 580 8 slot backplane

Backplane contains 8 rows for use in C8P style cases.
OSI 581 board OSI581 Board Model 581 17 slot backplane

Backplane contains 17 rows for use in C3 style long cases.
OSI 582 board OSI582 Board

(Image courtesy Sarkis Daniel)
Model 582 4 slot backplane

Backplane contains 4 rows for use in C4P style cases.
OSI 583 board OSI583 Board Model 583 18 slot backplane

Backplane contains 18 rows for use in C3 style long cases.
OSI board OSI590 Hard disk ctrl Model 590 Hard Disk Interface & memory controller © 1981

Contains 12 pin board connector for OSI 596 and 2 16 pin headers for cable from OSI 596 Contains 2nd OSI 48 bus for connection to OSI 525 dual port static ram board.

OSI590 schematics

OSI hard disk interface board OSI592 Hard disk interface

(Image courtesy of Ron Bihler)

Model 592 Okidata Hard Disk Interface © 1977

Used with CD-74 74MB Winchester disk drive
OSI hard disk interface board OSI594 Hard disk interface Model 594 Shugart Hard Disk Interface © 1980

Used with CD-23 29MB Winchester disk drive
OSI hard disk ctrl board OSI596 Hard disk interface Model 596 Hard Disk Interface © 1980

Contains 50 pin cable to Shugart SA 1004 Hard Disk 20 pin cable to attach to Hard Disk controller (SA1000?) 12 pin plug bridges to 590 Also has 2 16 pin cable to attach to OSI 590 board Disk controller interface (SA1000?) attaches to top of this board
OSI 598 board OSI598 Hard disk ctrl Model 598 Hard disk controller for Shugart SA1004 © 1982

Contains interface to directly connect to Shugart SA1004 8" hard disk 8K of 2114 RAM One 50 pin cable header and one 20 pin cable header connect to SA1004
OSI Complete system  board OSI600 Super Board Model 600 SuperBoard II © 1978 &
Model 600D Superboard II © 1980

Complete computer on one circuit board. Contains 6502 CPU, RAM, ROM, BASIC in ROM, Keyboard, Cassette & video out
Video arranged in 32x32 display, 24x24 visible.
Keyboard $DFxx (uses inverted values compared to 540 polled KB interface, bit is 0 when key pressed)

Superboard II Supports 64x16 display (48x12 visible), Sound Output (DAC) with Color video expansion option and Populated RS-232

OSI600 schematics

OSI board OSI610 Expansion Board Model 610 disk expansion for 600 board © 1978

Contains disk controller & decoder logic similar to 470 board along with up to 24K static RAM. Used for expansion and real time clock functionality
The 600 board + 610 board are used togeher with a floppy drive to make a C1PMF

OSI610 schematics

OSI 620 bus expander board OSI620 Bus Expander Model 620 Superboard bus expander

Contains 40 pin socket for connection to OSI 600/610 board and buffers to interface to OSI48 backplane board (OSI480, OSI582) for additonal expansion.

OSI620 schematics

OSI 630 color board OSI630 color video Model 630 Superboard color video expander

Color generator and RAM for C1 series II
OSI A12 board A12 board A12 interface board © 1977

Disk cable connector board for 470 Disk controller
OSI A13 board A13 board A13 interface board © 1979

Disk cable connector board for 505CPU board
OSI A15 board A15 board A15 interface board © 1979

Interface board for Joystick, Modem & Printer, 16 PIA lines, 16bit Head End card I/O.
Populated with two DB25 connectors for serial I/O, four DB9 connectors for joysticks etc., and three 16Pin sockets for Head End cards. Interfaces to OSI 505B board via 40pin socket and ribbon cable, interfaces to OSI 542 keyboard via 16pin ribbon cable. Used in C4P-MF, C4P-DMF, & C8P-DF systems.
OSI CA-15V board CA-15V Telephone Interface
** Large Image Needed!
CA-15V Universal Telephone interface

The Universal Telephone Interface provides the host computer with general purpose telephone communications capability. Includes 300 baud internal modem. Generates and decodes Touch-Tone signals. Includes multiplexers to route spoken voice out to external devices like recorders, voice recognition circuts, A/D converters and can accept spoken words from several sources to the telephone.
OSI CA-25 board CA-25 Security Interface
CA-25 Security and AC remote interface

Head End card, security and AC remote interface connects the AC-17P home security system and AC-12P wireless remote control system (X10) to C2 and C3 computers. (Interfaces to ultrasonic sensor input on BSR X-10 controller)