N8VEM was a homebrew computing project. 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 hobbyists. 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 the N8VEM project was ended by its creator Andrew Lynch 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 demonstrati ...

carrying a

Z80 The Z80 is an 8-bit microprocessor introduced by Zilog as the startup company's first product. The Z80 was conceived by Federico Faggin in late 1974 and developed by him and his 11 employees starting in early 1975. The first working samples were ...

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/ 85-based microcomputers by Gary Kildall of Digital Research, Inc. Initial ...

and similar operating systems. It was created in 2008 by Andrew Lynch. Contrasted with the

P112 The P112 is a stand-alone 8-bit CPU board. Typically running CP/M or a similar operating system, it provides a Z80182 (Z80 upgrade) CPU with up to 1MB of SRAM memory, 32KB of in-system programmable flash ROM, serial, parallel and diskette IO, and a ...

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

Z180 The Zilog Z180 eight-bit processor is a successor of the Z80 CPU. 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 generator, 16-bit coun ...

Intel 80188 The Intel 80188 microprocessor was a variant of the Intel 80186. The 80188 had an 8-bit external data bus instead of the 16-bit bus of the 80186; this made it less expensive to connect to peripherals. The 16-bit registers and the one megabyte add ...

MOS 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 microprocessor that was designed by a small te ...

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 6 ...

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 general ...

. The N8VEM boards are 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. It features an integrated environment for schematic capture, PCB layout, manufacturing file viewing, S ...

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 printed wiring board or PWB) is a medium used in Electrical engineering, electrical and electronic engineering to connect electronic components to one another in a controlled manner. It takes the form of a L ...

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

8085 The Intel 8085 ("''eighty-eighty-five''") is an 8-bit microprocessor produced by Intel and introduced in March 1976. It is software-binary compatible with the more-famous Intel 8080 with only two minor instructions added to support its added i ...

assembly language In computer programming, assembly language (or 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 be ...

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 ope ...

Telemark Cross Assembler program (TASM), as well as the open source

Small Device C Compiler The Small Device C Compiler (SDCC) is a free-software, partially retargetable C compiler for 8-bit microcontrollers. It is distributed under the GNU General Public License. The package also contains an assembler, linker, simulator and debugger. ...

. 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 (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/output lines with a variety of pr ...

PPI chips. The design philosophy encourages low cost development and assembly by hobbyist amateurs using common tools such as 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 i ...

multimeter A multimeter is a measuring instrument that can measure multiple electrical properties. A typical multimeter can measure voltage, resistance, and current, in which case it is also known as a volt-ohm-milliammeter (VOM), as the unit is equipped w ...

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

oscilloscope An oscilloscope (informally a scope) is a type of electronic test instrument that graphically displays varying electrical voltages as a two-dimensional plot of one or more signals as a function of time. The main purposes are to display repetiti ...

is recommended but not required. Some basic electronic 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, allow 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 has collaborated in developing a range of boards for the

S-100 bus The S-100 bus or Altair bus, IEEE 696-1983 ''(withdrawn)'', is an early computer bus designed in 1974 as a part of the Altair 8800. The bus was the first industry standard expansion bus for the microcomputer industry. computers, consisting of ...

. 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 initial design work has been 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 other board projects aim to apply the convenient bus architecture to processor families beyond the 8080/Z80 CPUs for which the bus standard was originally designed: notably 6502, 68000, and later Intel processor types. 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 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 oth ...

, many of whom are actively involved in designing and prototyping the hardware and

software Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work. At the lowest programming level, executable code consists ...

. 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 asp ...

frequented by

Steve Wozniak Stephen Gary Wozniak (; born August 11, 1950), also known by his nickname "Woz", is an American electronics engineer, computer programmer, philanthropist, inventor, and technology entrepreneur. In 1976, with business partner Steve Jobs, he c ...

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 Google Groups is a service from Google that provides discussion groups for people sharing common interests. The Groups service also provides a gateway to Usenet newsgroups via a shared user interface. Google Groups became operational in February ...

and

Wiki A wiki ( ) is an online hypertext publication collaboratively edited and managed by its own audience, using a web browser. A typical wiki contains multiple pages for the subjects or scope of the project, and could be either open to the pu ...

Software Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work. At the lowest programming level, executable code consists ...

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

and freely available for download from the

. 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 on ...

simulates the N8VEM SBC (along with many other architectures), providing a virtualised 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) 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 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 CD or DVD drives. The connection ...

) drive expansion) *

Zilog Zilog, Inc. is an American manufacturer of microprocessors and 8-bit and 16-bit microcontrollers. It is also a supplier of application-specific embedded system-on-chip (SoC) products. Its most famous product is the Z80 series of 8-bit microp ...

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 IMAGE:TMS9928A 01.jpg, VDP TMS9928A The TMS9918 is a video display controller (VDC) manufactured by Texas Instruments, in manuals referenced as 'Video Display Processor' (VDP ...

AY-3-8910 The AY-3-8910 is a 3-voice programmable sound generator (PSG) designed by General Instrument in 1978, initially for use with their 16-bit General Instrument CP1600, CP1610 or one of the PIC1650 series of 8-bit microcomputers. The AY-3-8910 and ...

, 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 PC industry within three years. The term can no ...

PS/2 The Personal System/2 or PS/2 is IBM's second generation of personal computers. Released in 1987, it officially replaced the IBM PC, XT, AT, and PC Convertible in IBM's lineup. Many of the PS/2's innovations, such as the 16550 UART (serial po ...

keyboard,

mouse, micro SD (

Secure Digital Secure Digital, officially abbreviated as SD, is a proprietary format, proprietary non-volatile memory, non-volatile Flash memory, flash memory card format developed by the SD Association, SD Association (SDA) for use in portable devices. The s ...

), prototyping area) *

Cassette Cassette may refer to: Technology * Cassette tape (or ''musicassette'', ''audio cassette'', ''cassette tape'', or ''tape''), a worldwide standard for analog audio recording and playback ** Cassette single (or "Cassingle"), a music single in the ...

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 Cartridge reader (load contents of MSX cartridges) * MSX 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

socket adapter (connect ECB boards directly to

CPU) * 6x0x host processor (

Motorola 6800 The 6800 ("''sixty-eight hundred''") is an 8-bit computing, 8-bit microprocessor designed and first manufactured by Motorola in 1974. The MC6800 microprocessor was part of the Motorola 6800 family, M6800 Microcomputer System (latter dubbed ''68xx' ...

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 microprocessor that was designed by a small t ...

CPU 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