The COMX-35 was a

home computer Home computers were a class of microcomputers that entered the market in 1977 and became common during the 1980s. They were marketed to consumers as affordable and accessible computers that, for the first time, were intended for the use of a s ...

that was one of the very few systems to use the

RCA 1802 The COSMAC (Complementary Symmetry Monolithic Array Computer) is an 8-bit microprocessor family introduced by RCA. It is historically notable as the first CMOS microprocessor. The first production model was the two-chip CDP1801R and CDP1801U, whi ...

microprocessor A microprocessor is a computer processor (computing), processor for which the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, a ...

, the same microprocessor that is also used in some

space probe Uncrewed spacecraft or robotic spacecraft are spacecraft without people on board. Uncrewed spacecraft may have varying levels of autonomy from human input, such as remote control, or remote guidance. They may also be autonomous, in which th ...

s. The COMX-35 had a keyboard with an integrated

joystick A joystick, sometimes called a flight stick, is an input device consisting of a stick that pivots on a base and reports its angle or direction to the device it is controlling. Also known as the control column, it is the principal control devic ...

in place of cursor keys. It was relatively inexpensive and came with a large collection of software. COMX-35 was manufactured in

Hong Kong Hong Kong)., Legally Hong Kong, China in international treaties and organizations. is a special administrative region of China. With 7.5 million residents in a territory, Hong Kong is the fourth most densely populated region in the wor ...

by ''COMX World Operations Ltd'' and was released in the

Netherlands , Terminology of the Low Countries, informally Holland, is a country in Northwestern Europe, with Caribbean Netherlands, overseas territories in the Caribbean. It is the largest of the four constituent countries of the Kingdom of the Nether ...

the United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

Sweden Sweden, formally the Kingdom of Sweden, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east. At , Sweden is the largest Nordic count ...

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

Finland Finland, officially the Republic of Finland, is a Nordic country in Northern Europe. It borders Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of Bothnia to the west and the Gulf of Finland to the south, ...

Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. The remote Arctic island of Jan Mayen and the archipelago of Svalbard also form part of the Kingdom of ...

Italy Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...

Singapore Singapore, officially the Republic of Singapore, is an island country and city-state in Southeast Asia. The country's territory comprises one main island, 63 satellite islands and islets, and one outlying islet. It is about one degree ...

Turkey Turkey, officially the Republic of Türkiye, is a country mainly located in Anatolia in West Asia, with a relatively small part called East Thrace in Southeast Europe. It borders the Black Sea to the north; Georgia (country), Georgia, Armen ...

and

the People's Republic of China ''The'' is a grammatical Article (grammar), article in English language, English, denoting nouns that are already or about to be mentioned, under discussion, implied or otherwise presumed familiar to listeners, readers, or speakers. It is the ...

Hardware

Technical specifications

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 ...

: RCA CDP1802 at or (NTSC) *

Random-access memory Random-access memory (RAM; ) is a form of Computer memory, electronic computer memory that can be read and changed in any order, typically used to store working Data (computing), data and machine code. A random-access memory device allows ...

: ( max) *

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 * ...

: with

BASIC Basic or BASIC may refer to: Science and technology * BASIC, a computer programming language * Basic (chemistry), having the properties of a base * Basic access authentication, in HTTP Entertainment * Basic (film), ''Basic'' (film), a 2003 film ...

interpreter *VIS: ( Video Interface System) RCA CDP1869/CDP1870 **Text modes: 40 columns x 24 lines. Alternative , and **Character set: 128 Programmable characters, the default character set displayed only uppercase characters **Character size: 6x9 (PAL) or 6x8 (NTSC) pixels, alternative up to 6x16 **Graphics modes: None, but the character-set was re programmable to simulate a High Resolution display **Colours: A total of 8 foreground colours are available (with a limited choice of 4 per character and 1 per line of that character) and 8 background colours (defined for the whole screen). *Sound: RCA CDP1869 **2 channels: one for tone generation with a span of 8

octave In music, an octave (: eighth) or perfect octave (sometimes called the diapason) is an interval between two notes, one having twice the frequency of vibration of the other. The octave relationship is a natural phenomenon that has been referr ...

s, and 1 for special effect/white noise. Volume programmable in 16 steps.

Memory map

Memory

The COMX-35 has of RAM. It consists of of User RAM of which roughly is available for BASIC code, with the rest reserved for use by the BASIC System ROM. The remaining of RAM is used by the Video Interface System.

Video interface system

The COMX-35 uses the RCA CDP1869 and CDP1870 Video Interface System (VIS), consisting of the CDP1869 address and sound generator and the CDP1870 colour video generator. The COMX-35 automatically detects the

refresh rate The refresh rate, also known as vertical refresh rate, vertical scan rate or vertical frequency in reference to terminology originating with the cathode-ray tubes (CRTs), is the number of times per second that a raster-based display device displa ...

. The VIS runs on in

PAL Phase Alternating Line (PAL) is a color encoding system for analog television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields (25 ...

and in

NTSC NTSC (from National Television System Committee) is the first American standard for analog television, published and adopted in 1941. In 1961, it was assigned the designation System M. It is also known as EIA standard 170. In 1953, a second ...

. This frequency is halved and used to clock the CPU. The VIS is also responsible for the timing of the interrupts and non display period. Video memory can only be accessed during the non display period, which allows for execution of 2160 machine cycles in

and 1574 cycles in

. To maximize access to the Video memory, the program can be paused until the non display period by checking EF1 in a loop. The Video memory is divided into RAM character memory and RAM page memory. The page memory stores the ASCII code for each character position on the screen. The screen had 960 characters where position 0 (left top corner) could be accessed by memory location @F800 (before scrolling). The character memory stored the character definition of each ASCII character and can be accessed at memory locations @F400-@F7FF.

Models

The COMX-35 came in two colours, with either a white or black keyboard. Later models also included a monitor port. A second model called the COMX PC1 improved the keyboard and added a joystick port. A clone known as the Savla PC1 was sold in

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

Peripherals

The COMX-35 has one 44-pin external connector for additional expansion options in the form of interface cards. A section of memory is reserved for use by any interface card. The following hardware was available: ; Expansion box: The expansion box allowed up to four interface cards to be connected to the COMX-35. The expansion box also included a

firmware In computing Computing is any goal-oriented activity requiring, benefiting from, or creating computer, computing machinery. It includes the study and experimentation of algorithmic processes, and the development of both computer hardware, h ...

ROM connected to memory location @E000-@EFFF which extended basic with commands and logic to switch between different interface cards. ; Floppy disk controller: The COMX Floppy disk controller allowed connection of 5.25" disk drives. The controller used the WD1770 clocked at . The DOS ROM was selected between address C000-DFFF and was also mapped over address DD0-DDF of the basic ROM. COMX DOS supports 35 tracks for both single and double sided disks and 70 tracks on single sided disks. Every track consisted of 16 sectors and every sector of 128 bytes, resulting in disk files of max . ; Printer card: The COMX Printer card allowed connection of parallel and serial printers. Depending on what type of printer was connected the firmware ROM was selected either with the parallel firmware between memory location @C000-@CFFF and the serial firmware between memory location @D000-@DFFF or the other way around. ; Thermal printer and card: The COMX Thermal Printer came including a dedicated interface card, printing was done on thermal paper by using a head that with which could heat the paper and as such print both text and images. You needed to be careful when writing your own printer drivers, which was needed for graphic printing, as it was very easy to 'burn' the printer head. ; 32K RAM card: The COMX RAM card placed additional RAM from address @C000 to @DFFF, i.e. only one bank of the available at a time. To switch to a different bank the OUT 1 instruction needed to be used via 1802 assembler code. Bit 5 and 6 were used for the RAM bank selection (bit 1 to 4 were used for the expansion box slot selection). ; 80-column card: The COMX 80-column card added possibility to use basic with a text mode of . The

MC6845 The Motorola 6845, or MC6845, is a display controller that was widely used in 8-bit computers during the 1980s. Originally intended for designs based on the Motorola 6800 CPU and given a related part number, it was more widely used alongside var ...

was used as video chip. ; F&M Joy Card: The F&M Joy card was a third-party expansion card which was made in a small quantity. The card had connections for 2 joysticks and came with a simple game and supporting software.

Software

A screenshot from ''Trainspotting'' A screenshot from ''Get your gadget'' West Electronics, the company importing the COMX-35 in The Netherlands, provided most of their software for free and without copyrights (or for a small fee for tape, disk and/or shipment). West Electronics also organized different competitions for homebrew software. Homebrew development for the COMX-35 is still active in The Netherlands as a result. The most popular game on the COMX-35 was 'Worm' (known in The Netherlands as 'Eet een wurm'). This was a very basic adaptation of ''

Snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...

''. Playing the game long enough would eventually cause it to run out of places to place new food, slowing the game down.

Known bugs

One can crash the COMX-35 by simply typing 65535 as the line number in BASIC. The BASIC interpreter can be put into a hard-lock by pressing the return key while the 'READY' prompt is displayed. This is because the prompt is treated as a 'READ' command, despite the lack of DATA statements in the program. The '!' symbol in the character set displays a red dot just above the black dot.

Emulator

Emma 02 is capable of emulating the COMX-35 along with other systems which share a similar chip-set.

References

{{Reflist Home computers 8-bit computers Computer-related introductions in 1983