The Compukit UK101
microcomputer
A microcomputer is a small, relatively inexpensive computer having a central processing unit (CPU) made out of a microprocessor. The computer also includes memory and input/output (I/O) circuitry together mounted on a printed circuit board (PC ...
(1979) is a kit
clone of the
Ohio Scientific
Ohio Scientific Inc. (also known as Ohio Scientific Instruments) was an Ohio-based computer company that built and marketed microcomputers from 1975 to 1981. Their best-known products were the Challenger series of microcomputers and Superboard si ...
Superboard II
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 ...
, with a few enhancements for the
UK market - notably replacing the 24×24 (add guardband kit to give 32×32) screen display with a more useful 48×16 layout working at
UK video frequencies. The video output is black and white with 256 characters
generated by a two
kilobyte
The kilobyte is a multiple of the unit byte for digital information.
The International System of Units (SI) defines the prefix ''kilo'' as 1000 (103); per this definition, one kilobyte is 1000 bytes.International Standard IEC 80000-13 Quantiti ...
ROM
Rom, or ROM may refer to:
Biomechanics and medicine
* Risk of mortality, a medical classification to estimate the likelihood of death for a patient
* Rupture of membranes, a term used during pregnancy to describe a rupture of the amniotic sac
* R ...
. It has no bit-mapped graphics capability. The video is output through a
UHF modulator, designed to connect to a TV set.
History
The UK101 design was published in Practical Electronics, a popular hobbyists magazine at the time. The August, September, October and November 1979 issues carried the four parts of the article, credited to "Dr A. A. Berk". Later issues of the magazine contained information on modifications and additions to the machine, including a series of articles on building an expansion unit.
Kits of parts for building the machine were available from CompShop Ltd of 14 Station Road, Barnet, Hertfordshire. It is thought that around 5000 kits were produced.
Description
Processor
The Compukit UK101 is powered by a
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 ...
microprocessor CPU running at 1
MHz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...
, and is equipped with up to 8
kilobytes
The kilobyte is a multiple of the unit byte for digital information.
The International System of Units (SI) defines the prefix ''kilo'' as 1000 (103); per this definition, one kilobyte is 1000 bytes.International Standard IEC 80000-13 Quantitie ...
of
RAM
Ram, ram, or RAM may refer to:
Animals
* A male sheep
* Ram cichlid, a freshwater tropical fish
People
* Ram (given name)
* Ram (surname)
* Ram (director) (Ramsubramaniam), an Indian Tamil film director
* RAM (musician) (born 1974), Dutch
* Ra ...
using 2114
static RAM
Static random-access memory (static RAM or SRAM) is a type of random-access memory (RAM) that uses latching circuitry (flip-flop) to store each bit. SRAM is volatile memory; data is lost when power is removed.
The term ''static'' differen ...
chips of 1024×4-bit. An additional memory-mapped 1 KB of RAM is used for the video display. It has the
8K Microsoft BASIC interpreter stored in
ROM
Rom, or ROM may refer to:
Biomechanics and medicine
* Risk of mortality, a medical classification to estimate the likelihood of death for a patient
* Rupture of membranes, a term used during pregnancy to describe a rupture of the amniotic sac
* R ...
. In addition to Basic, a 6502 machine code monitor (2K bytes) is built into ROM. It allows programming by entering sequences of 6502
opcode
In computing, an opcode (abbreviated from operation code, also known as instruction machine code, instruction code, instruction syllable, instruction parcel or opstring) is the portion of a machine language instruction that specifies the operat ...
s. Later a
two-pass assembler
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 ...
was available which allows the use of assembly language.
Although the 6502 has two interrupt input pins (NMI and IRQ), neither is used by the UK101.
Display
The UK101 has a 16-row, 48-column
memory-mapped character
semigraphics
Text-based semigraphics or pseudographics is a primitive method used in early text mode video hardware to emulate raster graphics without having to implement the logic for such a display mode.
There are two different ways to accomplish the emu ...
display, with each character taking up 8x8 pixels with an aspect ratio of about 1:2.
All
scrolling
In computer displays, filmmaking, television production, and other kinetic displays, scrolling is sliding text, images or video across a monitor or display, vertically or horizontally. "Scrolling," as such, does not change the layout of the text ...
and character output functions are handled by firmware. In the original ROMs, the output functions were rudimentary and did not include a clear-screen function. CPU access to video memory causes noticeable glitches (known as "snow") on the screen.
Keyboard
The keyboard of the UK101 is located on the main PCB, and comprises a matrix of keyswitches. The matrix is interfaced to the CPU via two 8-bit I/O ports, and is polled by firmware in the machine's ROMs. One key is a latching type, the shift-lock key. When supplied as a kit, the keyboard was assembled by the purchaser from a bag of switches and keytops.
The keyboard ports are located at address DF00 (
hex), or 57088 (decimal). BASIC programs typically poll for real-time keyboard input by using the PEEK and POKE commands at that address. Because the keyboard lacks any way to generate an interrupt, it is not possible to implement a
typeahead
Typeahead is a feature of computers and software (and some typewriters) that enables users to continue typing regardless of program or computer operation—the user may type in whatever speed is desired, and if the receiving software is busy at th ...
buffer. The keyboard matrix also lacks any diodes at the intersections of the matrix. This leads to problems when reading certain combinations of keys pressed simultaneously. The matrix was designed to allow only the shift, control and shift-lock keys to be pressed simultaneously with another key. The keyswitches themselves were originally manufactured by Cherry.
Program Storage
In common with other home computers of the time, software can be saved and loaded on standard cassette tapes. The UK101 uses the
Kansas City standard
The Kansas City standard (KCS), or ''Byte'' standard, is a data storage protocol for standard cassette tapes at . It originated in a symposium sponsored by Byte (magazine), ''Byte'' magazine in November 1975 in Kansas City, Missouri to develop a ...
tape format.
I/O is managed by a Motorola 6850
ACIA. This allows a full
RS-232
In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such a ...
port to be implemented, with the addition of a few extra components and minor modifications to existing jumpers on the board.
Compared to the Superboard
Although very similar to the Ohio Scientific Superboard II, the Compukit UK101 differed from that machine in a few places:
# Video display of the UK101 works at UK frequency and resolution.
# RF output is UHF, to suit domestic TVs in the UK.
# Power supply is located on the main PCB and accepts UK 240 V AC mains input (via a transformer).
# Display improved to 48 characters per line
# Memory increased to 8 KB
However, similarities in the PCB layout make it clear that this machine is a clone. The people involved with the modifications were
Chris Cary and Bill Wood.
Expansion
The 40 pin expansion socket opened up the world to the UK101. One could attach a dual floppy disk controller (5.25") and a memory expansion card (40K max) to allow faster and reliable save/load of programs/data.
A sound card became available, built around the
General Instrument 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 CP1610 or one of the PIC1650 series of 8-bit microcomputers. The AY-3-8910 and its variants were used i ...
, which together with a Peripheral Interface Adapter (PIA)
WDC 65C21
The W65C21S is a very flexible Peripheral Interface Adapter (PIA) for use with WDC’s 65xx and other 8-bit microprocessor families. It is produced by Western Design Center (WDC).
The W65C21S provides programmed microprocessor control of up to tw ...
chip, gave the UK101 audio abilities.
The UK101 floppy disk interface utilised a PIA to control the floppy disk drive stepper motor and another ACIA to serialise the data written to the disk.
A disk operating system was used to provide file storage capability but this resided in RAM and so reduced the available program space.
Typically single or double sided 40 track floppy drives could be supported.
The power consumption of an expanded UK101 could require up to 5Amps at 5.0Vdc (25Watts), so heat dissipation and power supply de-coupling were common challenges. Compare with a modern ARM microcontroller with similar capability at 0.5 Watts.
References
{{reflist
External links
Compukit UK101 Home Page– At BeeJay's home page
Ian's Compukit Home Page
Early microcomputers
6502-based home computers
Computers designed in the United Kingdom
Home computers
Products introduced in 1979