Comx-35
Encyclopedia
The COMX-35 was a home computer
that was one of the very few systems to use the RCA 1802
microprocessor
, the same microprocessor that is also used in some space probes. From the outset the 1802 has also been available fabricated in Silicon on Sapphire
semiconductor process technology, which gives it a degree of resistance to radiation and electrostatic discharge
.
The COMX-35 had a keyboard with an integrated joystick
in place of cursor keys. It was relatively inexpensive and came with a large collection of software. COMX-35 was manufactured in Hong Kong
by COMX World Operations Ltd.
The COMX automatically selected operation in PAL
or NTSC
, this was done via the PAL/NTSC input on the VIS. Also during start-up the system ROM detected PAL/NTSC by checking EF2. EF2 gave PAL/NTSC information before the first pulse on the Q line, after this EF2 was used for keyboard handling.
The VIS ran on for a PAL and for an NTSC machine. This frequency was divided by 2 and output via CPUCLK (pin 38) to the CDP 1802 for timing of the CPU (2.813 and ). The VIS was also responsible for the timing of the interrupt and timing of the non display period via PREDISPLAY (pin 1). Video memory could only be accessed during the non display period which allowed for execution of 2160 machine cycles on a PAL and 1574 on an NTSC machine. Provided that not more instructions were executed than the indicated maximum number of machine cycles video memory could be accessed during the interrupt routine. Alternatively the program could be paused by waiting for a non display period by checking EF1.
The Video memory consisted of 2 parts, RAM page memory and RAM character memory.
The page memory stored 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 could be accessed by memory location @F400-@F7FF. Character memory could be accessed via different methods see also the VIS data sheet.
ROM connected to memory location @E000-@EFFF which extended basic with commands and logic to switch between different interface cards. Next to the standard firmware ROM there was an adaptation made by F&M (Frank and Marcel van Tongeren) this ROM added a screen editor feature to COMX basic.
Probably the most popular game on the COMX was 'Worm' known in The Netherlands as 'Eet een wurm'. This was a very basic game where you had to direct a snake over the screen and eat all the worms. If you managed to play 'Worm' long enough it would eventually run out of places to put new 'food' and as such slow down the game almost to a stop. There was a correction made for the game by F&M including some additional improvements.
The COMX was probably most popular in The Netherlands mainly due to the efforts from West Electronics to provide free software. As a result of the competitions quite a few excellent games were written by enthusiastic users like:
and many more!
, COSMAC ELF
, Netronis Elf II, Quest Super Elf, RCA Studio II
, Victory MPT-02, Visicom COM-100, Cidelsa, Telmac TMC-600
, Telmac TMC-2000, Telmac Nano, Pecom 64
and the ETI-660.
A similar thing as when using line number 65535 was typing in 'READY', after this the COMX was not 'READY' anymore. F&M discovered this one when they designed the F&M screen editor and pressed 'CR' (return) on the 'READY' prompt. As such they decided to change the prompt into 'OK' to avoid too many accidental hangings when using a screen editor. This fault was actually caused by the basic READ command, when a READ Y (or any other READ) instruction is given when there is no DATA statement in the loaded basic program the COMX hangs.
Another bug in the standard character set was the '!' which displayed a red dot just above the black dot.
Home computer
Home computers were a class of microcomputers entering the market in 1977, and becoming increasingly 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 single nontechnical user...
that was one of the very few systems to use the RCA 1802
RCA 1802
The RCA CDP1802, also known as the COSMAC , is an 8-bit CMOS microprocessor introduced by RCA in early 1976. It is being by Intersil Corporation as a high-reliability microprocessor...
microprocessor
Microprocessor
A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...
, the same microprocessor that is also used in some space probes. From the outset the 1802 has also been available fabricated in Silicon on Sapphire
Silicon on sapphire
Silicon on sapphire is a hetero-epitaxial process for integrated circuit manufacturing that consists of a thin layer of silicon grown on a sapphire wafer. SOS is part of the Silicon on Insulator family of CMOS technologies...
semiconductor process technology, which gives it a degree of resistance to radiation and electrostatic discharge
Electrostatic discharge
Electrostatic discharge is a serious issue in solid state electronics, such as integrated circuits. Integrated circuits are made from semiconductor materials such as silicon and insulating materials such as silicon dioxide...
.
The COMX-35 had a keyboard with an integrated joystick
Joystick
A joystick 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. Joysticks, also known as 'control columns', are the principal control in the cockpit of many civilian and military aircraft, either as a center stick or...
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
Hong Kong is one of two Special Administrative Regions of the People's Republic of China , the other being Macau. A city-state situated on China's south coast and enclosed by the Pearl River Delta and South China Sea, it is renowned for its expansive skyline and deep natural harbour...
by COMX World Operations Ltd.
Technical specifications
- CPUCentral processing unitThe central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
: CDP 1802RCA 1802The RCA CDP1802, also known as the COSMAC , is an 8-bit CMOS microprocessor introduced by RCA in early 1976. It is being by Intersil Corporation as a high-reliability microprocessor...
at or (NTSC) - Random-access memoryRandom-access memoryRandom access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Strictly speaking, modern types of DRAM are therefore not random access, as data is read in...
: ( max) - ROMRead-only memoryRead-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...
: with BasicBASICBASIC is a family of general-purpose, high-level programming languages whose design philosophy emphasizes ease of use - the name is an acronym from Beginner's All-purpose Symbolic Instruction Code....
interpreter - VIS: (Video Interface SystemVideo Display ControllerA Video Display Controller or VDC is an integrated circuit which is the main component in a video signal generator, a device responsible for the production of a TV video signal in a computing or game system...
) 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: 2 channels: one for tone generation with a span of 8 octaveOctaveIn music, an octave is the interval between one musical pitch and another with half or double its frequency. The octave relationship is a natural phenomenon that has been referred to as the "basic miracle of music", the use of which is "common in most musical systems"...
s, and 1 for special effect/white noise. Volume progammable in 16 steps.
Memory map
| Address | Type |
|---|---|
| @0000-@3FFF | Basic system ROM |
| @4000-@43FF | System Parameters |
| @4400-@BDFF | Basic Program and Data storage |
| @BE00-@BFFF | Reserved for DOS |
| @C000-@DFFF | Interface card expansion ROM |
| @E000-@EFFF | Expansion box ROM |
| @F000-@F3FF | Not used |
| @F400-@F7FF | Character Memory |
| @F800-@FFFF | Screen Page Memory |
RAM
The 'COMX 35' was called '35' due to the amount of RAM in the machine, this included actual user RAM of which roughly was available for actual basic the rest was used for system parameters and reserved for use by the basic system ROM. An additional was included as video RAM, for details see the Video Interface System (VIS) chapter.Video interface system
The COMX used 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 automatically selected operation in PAL
PAL
PAL, short for Phase Alternating Line, is an analogue television colour encoding system used in broadcast television systems in many countries. Other common analogue television systems are NTSC and SECAM. This page primarily discusses the PAL colour encoding system...
or NTSC
NTSC
NTSC, named for the National Television System Committee, is the analog television system that is used in most of North America, most of South America , Burma, South Korea, Taiwan, Japan, the Philippines, and some Pacific island nations and territories .Most countries using the NTSC standard, as...
, this was done via the PAL/NTSC input on the VIS. Also during start-up the system ROM detected PAL/NTSC by checking EF2. EF2 gave PAL/NTSC information before the first pulse on the Q line, after this EF2 was used for keyboard handling.
The VIS ran on for a PAL and for an NTSC machine. This frequency was divided by 2 and output via CPUCLK (pin 38) to the CDP 1802 for timing of the CPU (2.813 and ). The VIS was also responsible for the timing of the interrupt and timing of the non display period via PREDISPLAY (pin 1). Video memory could only be accessed during the non display period which allowed for execution of 2160 machine cycles on a PAL and 1574 on an NTSC machine. Provided that not more instructions were executed than the indicated maximum number of machine cycles video memory could be accessed during the interrupt routine. Alternatively the program could be paused by waiting for a non display period by checking EF1.
The Video memory consisted of 2 parts, RAM page memory and RAM character memory.
The page memory stored 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 could be accessed by memory location @F400-@F7FF. Character memory could be accessed via different methods see also the VIS data sheet.
Models
The COMX 35 came in two colours, either a white or black keyboard. Later models also included a monitor connection. The second COMX home computer was called the COMX PC1 which was basically the same hardware as the COMX-35 with a better keyboard and a joystick connection.Peripherals
The COMX 35 had one 44-pin external connector for additional expansion options in the form of interface cards. Memory location @C000-DFFF was reserved for use by any interface card, either to connect ROM, additional RAM or for other purposes. The following HW was available:Expansion box
The expansion box allowed up to 4 interface cards to be connected to the COMX 35. The expansion box also included a firmwareFirmware
In electronic systems and computing, firmware is a term often used to denote the fixed, usually rather small, programs and/or data structures that internally control various electronic devices...
ROM connected to memory location @E000-@EFFF which extended basic with commands and logic to switch between different interface cards. Next to the standard firmware ROM there was an adaptation made by F&M (Frank and Marcel van Tongeren) this ROM added a screen editor feature to COMX basic.
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 was used as video chip.F&M Joy Card
This card was not developed by COMX but was a home made extension by F&M: only a handful were ever made. The card had connections for 2 joysticks and came with a simple game and supporting software.Software
The company importing the COMX in The Netherlands, West Electronics, provided almost all their software for the COMX for free and without copyrights (or for a small fee for tape, disk and/or shipment). West Electronics also organized different competitions for home made software.Games
The COMX was probably most popular in The Netherlands mainly due to the efforts from West Electronics to provide free software. As a result of the competitions quite a few excellent games were written by enthusiastic users like:
- Get Your Gadget by JunioR (Jeroen Griffioen and Robbert Nix)
- Boulderdash by AHON (Arjan Houben and Oscar Nooy)
- Donkey The Kong by MP-Soft (Michel Peters)
- Happiehap and Trainspotting by F&M (Frank and Marcel van Tongeren)
and many more!
Emulator
An emulator (Emma 02) running on Microsoft Windows is available and can be downloaded from the Dutch COMX Club site or the Emma 02 site. The screenshots shown here are generated with this emulator. The emulator also supports the following other 1802 systems: Elf 2000, COSMAC VIPCOSMAC VIP
The COSMAC VIP was an early microcomputer that was aimed at video games. For a price of US$275, it could be purchased from RCA by mail order. It came in kit form, and had to be assembled. Its dimensions were 22 x 28 cm, and it had a RCA 1802 processor; along with a crystal clock operating at 1.76...
, COSMAC ELF
COSMAC ELF
The COSMAC ELF was an RCA 1802 microprocessor-based computer based on a series of construction articles in Popular Electronics magazine in 1976 and 1977. Through the back pages of electronics magazines, both Netronics and Quest Electronics offered low-priced kits that were based on this design. ...
, Netronis Elf II, Quest Super Elf, RCA Studio II
RCA Studio II
The RCA Studio II is a videogame console made by RCA that debuted in January 1977. The graphics of Studio II games were black and white and resembled those of earlier Pong consoles and their clones. The Studio II also did not have joysticks or similar game controllers but instead used two ten...
, Victory MPT-02, Visicom COM-100, Cidelsa, Telmac TMC-600
Telmac TMC-600
The Telmac TMC-600 was a Finnish microcomputer produced during the early 1980s. It was introduced in 1982 by Telercas, the Finnish importer of RCA microchips. Only 600 units were produced, making it very rare today. The TMC-600 was the only commercially available microcomputer designed and...
, Telmac TMC-2000, Telmac Nano, Pecom 64
Pecom 64
Pecom 64 was an educational and/or home computer developed by Elektronska Industrija Niš of Serbia in 1985.- Specifications :* CPU: CDP 1802B 5V7 running at 2.813 MHz* ROM: 16 KB, with optional 16 KB upgrade containing enhanced editor and assembler...
and the ETI-660.
Known bugs
The most famous bug in the COMX basic ROM was when you typed in the line number 65535 this resulted in the COMX hanging and the screen getting all messed up which could be very frustrating if the user had spent hours typing in a BASIC program.A similar thing as when using line number 65535 was typing in 'READY', after this the COMX was not 'READY' anymore. F&M discovered this one when they designed the F&M screen editor and pressed 'CR' (return) on the 'READY' prompt. As such they decided to change the prompt into 'OK' to avoid too many accidental hangings when using a screen editor. This fault was actually caused by the basic READ command, when a READ Y (or any other READ) instruction is given when there is no DATA statement in the loaded basic program the COMX hangs.
Another bug in the standard character set was the '!' which displayed a red dot just above the black dot.