N8VEM was a homebrew computing project created in 2008 by Andrew Lynch. It featured a variety of free and open hardware and software. N8VEM builders made their own homebrew computer systems for themselves and shared their experiences with other homebrew computer

hobby A hobby is considered to be a regular activity that is done for enjoyment, typically during one's leisure time. Hobbies include collecting themed items and objects, engaging in creative and artistic pursuits, playing sports, or pursuing other ...

ists. N8VEM homebrew computer components are made in the style of vintage computers of the mid to late 1970s and early 1980s using a mix of classic and modern technologies. They are designed with ease of amateur assembly in mind. In November 2015, Lynch ended the N8VEM project, and the community reconvened under the new name of Retrobrew Computers.

Creation and operation

There are several N8VEM designs starting with a

single-board computer A single-board computer (SBC) is a complete computer built on a single circuit board, with microprocessor(s), memory, input/output (I/O) and other features required of a functional computer. Single-board computers are commonly made as demonst ...

carrying a

Zilog Z80 The Zilog Z80 is an 8-bit computing, 8-bit microprocessor designed by Zilog that played an important role in the evolution of early personal computing. Launched in 1976, it was designed to be Backward compatibility, software-compatible with the ...

microprocessor designed to run

CP/M CP/M, originally standing for Control Program/Monitor and later Control Program for Microcomputers, is a mass-market operating system created in 1974 for Intel 8080/Intel 8085, 85-based microcomputers by Gary Kildall of Digital Research, Dig ...

and similar operating systems. Contrasted with the P112, which has some

surface-mount Surface-mount technology (SMT), originally called planar mounting, is a method in which the electrical components are mounted directly onto the surface of a printed circuit board (PCB). An electrical component mounted in this manner is referred ...

components, the N8VEM SBC uses only

through-hole In electronics, through-hole technology (also spelled "thru-hole") is a manufacturing scheme in which leads on the components are inserted through holes drilled in printed circuit boards (PCB) and soldered to pads on the opposite side, either ...

components, consistent with the design philosophy that building should be within the skills and resources of non-professional hobbyists. The project also developed boards for other

CPU A central processing unit (CPU), also called a central processor, main processor, or just processor, is the primary processor in a given computer. Its electronic circuitry executes instructions of a computer program, such as arithmetic, log ...

s, including the

Zilog Z180 The Zilog Z180 is an 8-bit microprocessor designed by Zilog as a successor to the Z80. It is compatible with the large base of software written for the Z80. The Z180 family adds higher performance and integrated peripheral functions like clock g ...

, the

Intel 80188 Intel Corporation is an American multinational corporation and technology company headquartered in Santa Clara, California, and incorporated in Delaware. Intel designs, manufactures, and sells computer components such as central processing u ...

, the

MOS Technology 6502 The MOS Technology 6502 (typically pronounced "sixty-five-oh-two" or "six-five-oh-two") William Mensch and the moderator both pronounce the 6502 microprocessor as ''"sixty-five-oh-two"''. is an 8-bit computing, 8-bit microprocessor that was desi ...

, and the

Motorola 6809 The Motorola 6809 ("''sixty-eight-oh-nine''") is an 8-bit microprocessor with some 16-bit features. It was designed by Motorola's Terry Ritter and Joel Boney and introduced in 1978. Although source compatible with the earlier Motorola 6800, the ...

68000 The Motorola 68000 (sometimes shortened to Motorola 68k or m68k and usually pronounced "sixty-eight-thousand") is a 16/32-bit complex instruction set computer (CISC) microprocessor, introduced in 1979 by Motorola Semiconductor Products Sector ...

and

68030 The Motorola 68030 ("''sixty-eight-oh-thirty''") is a 32-bit microprocessor in the Motorola 68000 family. It was released in 1987. The 68030 was the successor to the Motorola 68020, and was followed by the Motorola 68040. In keeping with ge ...

. The N8VEM boards were designed with the free

KiCad KiCad ( ) is a free software suite for electronic design automation (EDA). It facilitates the design and simulation of electronic hardware for PCB manufacturing. It features an integrated environment for schematic capture, Printed circuit boar ...

electronic design automation Electronic design automation (EDA), also referred to as electronic computer-aided design (ECAD), is a category of software tools for designing Electronics, electronic systems such as integrated circuits and printed circuit boards. The tools wo ...

(EDA) toolset.

Printed circuit board A printed circuit board (PCB), also called printed wiring board (PWB), is a Lamination, laminated sandwich structure of electrical conduction, conductive and Insulator (electricity), insulating layers, each with a pattern of traces, planes ...

routing was provided by FreeRouting.net. Software is developed in Z80/ 8085

assembly language In computing, assembly language (alternatively assembler language or symbolic machine code), often referred to simply as assembly and commonly abbreviated as ASM or asm, is any low-level programming language with a very strong correspondence bet ...

using the

MS-DOS MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few op ...

Telemark Cross Assembler program (TASM), as well as the open source Small Device C Compiler. A major design goal is to use freely available tools to the maximum extent possible. The printed circuit board design is supplemented using component libraries available at KiCad Libraries, specifically the Zilog Z80 CPU and

Intel 8255 The Intel 8255 (or i8255) Programmable Peripheral Interface (computer science), Interface (PPI) chip was developed and manufactured by Intel in the first half of the 1970s for the Intel 8080 microprocessor. The 8255 provides 24 parallel input/ou ...

Programmable

Peripheral A peripheral device, or simply peripheral, is an auxiliary hardware device that a computer uses to transfer information externally. A peripheral is a hardware component that is accessible to and controlled by a computer but is not a core compo ...

Interface Interface or interfacing may refer to: Academic journals * ''Interface'' (journal), by the Electrochemical Society * '' Interface, Journal of Applied Linguistics'', now merged with ''ITL International Journal of Applied Linguistics'' * '' Inter ...

(PPI) chips. The design philosophy encourages low cost development and assembly by hobbyist amateurs using common tools such as a 25-watt

soldering iron A soldering iron is a hand tool used in soldering. It supplies heat to melt solder so that it can flow into the joint between two workpieces. A soldering iron is composed of a heated metal tip (the ''bit'') and an insulated handle. Heating is o ...

, a

multimeter A multimeter (also known as a multi-tester, volt-ohm-milliammeter, volt-ohmmeter or VOM, avometer or ampere-volt-ohmmeter) is a measuring instrument that can measure multiple electrical properties. A typical multimeter can measure voltage, elec ...

, a logic probe (optional), and common hand tools. An

oscilloscope An oscilloscope (formerly known as an oscillograph, informally scope or O-scope) is a type of electronic test instrument that graphically displays varying voltages of one or more signals as a function of time. Their main purpose is capturing i ...

is recommended but not required. Some basic electronics skills are helpful, although the printed circuit boards are designed for relative beginners. There are numerous N8VEM components available including ECB and S-100 backplane boards, allowing processor and expansion boards to be connected. Other components include video boards, disk controllers, peripheral expansion, and prototyping boards. In response to interest from members, the N8VEM homebrew computing project collaborated in developing a range of boards for the S-100 bus. These can be used to build new systems from scratch on that historic industry standard platform, or to restore and enhance vintage S-100 systems preserved from the 1970s and 1980s. Most of the S-100 board's initial design work was contributed by John Monahan of s100computers.com, with board layout, prototyping and testing contributed by Andrew Lynch and other N8VEM supporters. Some of these S-100 boards provide enhanced capabilities beyond what was available on original S-100 machines, some are replacements for historic S-100 boards, and others aim to apply the convenient bus architecture to processor families beyond the 8080/Z80 CPUs for which the bus standard was originally designed: notably, the 6502, the 68000, and later Intel CPUs. N8VEM is notable for being the largest and most active homebrew computing community in existence today. The project is entirely non-commercial and is made up of over 350 hobbyists, many of whom are actively involved in designing and prototyping the hardware and

software Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications. The history of software is closely tied to the development of digital comput ...

. The community is a modern-day version of the historic

Homebrew Computer Club The Homebrew Computer Club was an early computer hobbyist group in Menlo Park, California, which met from March 1975 to December 1986. The club had an influential role in the development of the microcomputer revolution and the rise of that aspec ...

frequented by

Steve Wozniak Stephen Gary Wozniak (; born August 11, 1950), also known by his nickname Woz, is an American technology entrepreneur, electrical engineer, computer programmer, philanthropist, and inventor. In 1976, he co-founded Apple Inc., Apple Computer with ...

and other pioneers of home computer development. Printed circuit boards of the mature designs are manufactured in small batches on a collective order basis, and distributed to members for the cost of the board manufacturing and shipping. The project does not provide complete kits—builders must procure their own parts to populate a board. Support is purely on a volunteer basis through a Google Group and

wiki A wiki ( ) is a form of hypertext publication on the internet which is collaboratively edited and managed by its audience directly through a web browser. A typical wiki contains multiple pages that can either be edited by the public or l ...

. Software is

open source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use and view the source code, design documents, or content of the product. The open source model is a decentrali ...

and freely available for download from the wiki. The project was careful to keep things within the reach of the amateur computer hobbyist by using low cost and readily available components that can be assembled with simple hand tools. In addition, notable freeware system emulator

SIMH SIMH is a free and open source, multi-platform multi-system emulator. It is maintained by Bob Supnik, a former DEC engineer and DEC vice president, and has been in development in one form or another since the 1960s. History SIMH was based o ...

simulates the N8VEM SBC (along with many other architectures), providing a virtualized development environment that has the speed and flexibility of modern hardware. Completed N8VEM hardware and software has frequently been displayed at Vintage Computer Festivals.

Single board computers

ECB Bus: # SBC V2 (Z80, UART, PPI, RAM with battery backup, ROM, RTC) # SBC-188 (80C188 10-25 MHz, UART, PPI, RAM with battery backup, ROM, RTC, FDC) # N8 Home Computer (Z8S180 33 MHz, UART, ROM, RTC, Dual Interrupt controllers, Floppy, SD Card, 1MB RAM, AY-3-8910 sound, TMS9918A video, ECB bus) # SBC Mark IV (Z180 processor, 512K SRAM, 512K Flash or 1MB EPROM, RTC, SD Card, 8-bit IDE, RS-232, RS-422, ECB bus) # KISS 68030 (68030 processor up to 32MHz, up to 256M DRAM, 32K SRAM, 512K Flash, ECB bus) # ZetaSBC (via the ECB Shim board) S-100 bus: # Z80 S-100 # m68k S-100 (In progress) # 8086 S-100 (In progress) # 6502/6809 ECB + carrier boards for other cpu's (?) Other: # SBC6120-RBC: A new edition of the Spare Time Gizmo
SBC6120 Model 2
updated to use easily available RAM and EEPROM components, only two PCB layers, and KiCAD.

ECB expansion peripherals

* ECB Backplane (compact stand alone with 8

DIN 41612 DIN 41612 was a DIN standard for electrical connectors that are widely used in rack based electrical systems. Standardisation of the connectors is a pre-requisite for open systems, where users expect components from different suppliers to operat ...

slots) * ECB Bus Monitor (single step, address trap, bus status) * Disk IO (FDC & IDE (

Parallel ATA Parallel ATA (PATA), originally , also known as Integrated Drive Electronics (IDE), is a standard interface designed for IBM PC-compatible computers. It was first developed by Western Digital and Compaq in 1986 for compatible hard drives and C ...

) drive expansion) *

Zilog Zilog, Inc. is an American manufacturer of microprocessors, microcontrollers, and application-specific embedded System on a chip, system-on-chip (SoC) products. The company was founded in 1974 by Federico Faggin and Ralph Ungermann, who were soo ...

Peripherals (CTC, DART, dual PIOs) * Video Display Unit (80×25 character mode video) * Prototyping board with IO decode (buffered with labeled signal connectors) * ECB Extended backplane (12 slot with 3U mounting features) * DSKY (monitor/boot loader Hex LED display and keypad) * Sprites, Color Graphics, & Sound (

TMS9918 IMAGE:TMS9918A 01.jpg, VDP TMS9918A IMAGE:TMS9918A 02.jpg, VDP TMS9918A The TMS9918 is a video display controller (VDC) manufactured by Texas Instruments, in manuals referenced as "Video Display Processor" (VDP) and introduced in 1979. The TMS9918 ...

AY-3-8910 The AY-3-8910 is a 3-voice programmable sound generator (PSG) designed by General Instrument (GI) in 1978, initially for use with their 16-bit CP1610 or one of the PIC1650 series of 8-bit microcomputers. The AY-3-8910 and its variants were u ...

, joystick/paddle interface) * Prop IO (

VGA Video Graphics Array (VGA) is a video display controller and accompanying de facto graphics standard, first introduced with the IBM PS/2 line of computers in 1987, which became ubiquitous in the IBM PC compatible industry within three years. T ...

, PS/2 keyboard, PS/2 mouse, micro SD (

Secure Digital Secure Digital (SD) is a proprietary, non-volatile, flash memory card format developed by the SD Association (SDA). Owing to their compact size, SD cards have been widely adopted in a variety of portable consumer electronics, including digi ...

), prototyping area) * Cassette Interface ( KCS audio cassettes) * 4MEM (4MB SRAM expansion for SBC-188) * PPIDE (SBC parallel expansion port IDE interface) * Juha SD (SBC SD card for mass storage) *

MSX MSX is a standardized home computer architecture, announced by ASCII Corporation on June 16, 1983. It was initially conceived by Microsoft as a product for the Eastern sector, and jointly marketed by Kazuhiko Nishi, the director at ASCII Corpo ...

Cartridge reader (load contents of

cartridges) *

Cartridge (8K, 16K, & 32K EPROMs) * μPD7220 V2 prototype (16 color video display) * RAM-Floppy (4MB SRAM floppy drive replacement) * 4PIO (64 GPIO input/output board) * ECB to

Z80 The Zilog Z80 is an 8-bit microprocessor designed by Zilog that played an important role in the evolution of early personal computing. Launched in 1976, it was designed to be software-compatible with the Intel 8080, offering a compelling altern ...

socket adapter (connect ECB boards directly to

CPU) * 6x0x host processor (

Motorola 6800 The 6800 ("''sixty-eight hundred''") is an 8-bit microprocessor designed and first manufactured by Motorola in 1974. The MC6800 microprocessor was part of the M6800 Microcomputer System (later dubbed ''68xx'') that also included serial and parall ...

with ECB interface) * 6x0x IO mezzanine (ACIA, dual PIA, PTC, power, and expansion bus interface) * 6x0x ECB backplane (use ECB peripherals with stand alone 6x0x system) There is an active community development forum (N8VEM Google Discussion Group) from which additional board designs have been developed. There is active development of new boards underway.

System software

RomWBW is a popular system software distribution written to execute on N8VEM hardware. The N8VEM family of hardware are primarily Z80 based microprocessor single board computers, as well as miscellaneous boards which may be combined and placed in an ECB-like bus, enabling the builder to create a custom computer system. These computers are primarily built from discrete components as were computers in the late 1970s and 1980s. The majority of the systems are Z80 based and use the CP/M-80 operating system that was developed in the late 1970s by Digital Research, Inc. The RomWBW system software is highly configurable and supports all of the Z80 based systems constructed with N8VEM components. The system software is entirely open source and is provided in both machine readable source form and as pre-built images for those wishing to program firmware chips for insertion in the boards. In addition to the fully implemented operating system with its BIOS (customized for the N8VEM hardware), there are several dozen utility programs that configure and verify the proper operation of system components such as persistent storage in the form of IDE Hard Drives, Compact Flash, and Secure Digital chips. The CP/M-80 BIOS is written in assembly language and is built using the TASM assembler. Utility programs are written in a variety of languages including assembler, Digital Research RMAC, Aztec C, and Digital Research PLI. These natively hosted programming languages, and tools such as WordStar (a popular editor of the time), execute under the CP/M operating system and read source files stored on memory disk or persistent media such as IDE devices or Compact Flash and Secure Digital devices through the use of an external adapter. The version 1.x distributions of the system software have been written in a very standard CP/M-80 way and over the course of a half dozen releases has reached a highly stable state supporting the most commonly built configurations in use. The version 2.x operating software was recently released and uses bank switched memory technology to achieve enhanced functionality. Due to the new technology, there are no practical limits on the number of drivers that can be built in. In the future, this will allow for dynamic configuration and will be much more flexible for the users, in many ways similar to the CP/M-80 Plus family of operating systems which also took advantage of memory paging. In the same way the hardware is open source, the software is provided in source form as well allowing users to both learn how software was written in the early days of microprocessors, but also to write new software using provided tools and documentation available both in the distribution, on the subversion server, and downloadable from a variety of public archives worldwide. The current owners of the Digital Research, Inc., operating systems and language software have licensed it for non-commercial use and the most comprehensive archives can be found at http://www.cpm.z80.de as well as other popular locations and mirrors. An alternative system BIOS, UNA BIOS, also exists. It has the advantage that a single ROM image can run on all Z80 and Z180 systems. An alternative CP/M implementation, UNA CP/M, takes advantage of UNA BIOS disk and device drivers.

References

External links