Data Sheets

Development System


Microtutor II


Quest Super Elf




Case History

CPU Suffix Codes

Chip Indentification


The RCA CDP1802 COSMAC microprocessor is a one-chip CMOS 8-bit register-oriented central processing unit introduced in 1976.

COSMAC 1802 user manual Voyager spacecraft Although the 1802 is now more than 30 years old, it continues to prove itself in many industrial and commercial applications. A persistent rumor identifies it as the furthest microprocessor from Earth, having been used on board the Voyager spacecraft. (Voyager 1 is now the furthest human-made object from the Earth, at more than 100 A.U. distance.) Certain versions of the chip were extremely resistant to cosmic ray upset, making it well-suited for use in space. However, design work for the Voyager and Viking series spacecraft began long before the 1802 was available; instead they used custom-engineered computers. The Galileo spacecraft, however, used several 1802 processors.

The 1802 was first popularized for hobby use in a 1976 Popular Electronics article that described the "COSMAC Elf" computer. Around the same time commercial companies began offering similar products based on the 1802.

The 1802 is interesting for a number of reasons, not the least of which is the fact that it uses static CMOS circuitry, meaning it has no minimum clock frequency. Also, most instructions execute in two clock cycles. It has sixteen general purpose registers, each of which are 16 bits wide. Any of these registers can be used as a program counter or an accumulator.

I am interested in collecting and preserving systems and documentation related to the 1802 microprocessor. If you have any equipment, manuals, parts or other items related to the 1802, please send me an e-mail!

[This is from a presentation given in February 1974.]

The architecture of COSMAC (Complementary-Symmetry Monolithic-Array Computer) provides an adequate but small instruction repertoire, emphasizes a strong input/output capability, and is organized to minimize the amount of external logic needed to build up a complete computer. Its heart is a 16x16 scratch pad; any reference to memory is made via one of these 16 registers. Addressible memory is 65,536 8-bit bytes. An eight-bit two-way data bus interconnects the processor, any mixture of RAM and ROM, and the peripheral devices. The CPU presents a 40-pin interface to the system;: the 8-bit data bus; eight lines for multiplexing out 16-bit addresses to RAM or ROM, clock, reset, and load controls; two signals to control memory read and write; three lines to signal the state of the CPU (fetching or executing an instruction, responding to interrupt or direct-memory-access request); two time pulses per machine cycle for peripheral logic use; four lines driven during execution of the input/output instruction; four external flags from the peripherals; three request lines, respectively, for interrupt, DMA in, DMA out; and three power lines, one of which defines the interface high signal level.

RCA produced a number of documents related to the COSMAC series of processors.

CPI-279   Understanding CMOS
Databook   RCA CMOS Microprocessors, Memories and Peripherals
MPL-200   RCA Microsystems 1800 Product Guide and Price List
MPM-102   Program Development Guide for the COSMAC Microprocessor
MPM-109   COSMAC Microtutor Manual
MPM-201C   User Manual for the CDP1802 COSMAC Microprocessor
MPM-202A   Timesharing Manual for the RCA CDP1802 COSMAC Microprocessor
MPM-206A   Fixed-Point Binary Arithmetic Subroutines for RCA COSMAC Microprocessors
MPM-207   Floating-Point Arithmetic Subroutines for RCA COSMAC Microprocessors
MPM-209   COSMAC Microtutor II Manual
MPM-212   Instruction Manual for RCA COSMAC Microterminal
MPM-217   RCA COSMAC Floppy Disk System II CDP18S805 Instruction Manual
MPM-224   Instruction Manual for the RCA COSMAC Evaluation Kit CDP18S020 and the EK/Assembler-Editor Design Kit CDP18S024
VIP-330   RCA COSMAC VIP Instruction Manual for VP-111
VIP-565   VIP EPROM Programmer VP565 Instruction Manual

Programmer's Guide to the 1802, Tom Swan, Hayden Publishing, 1981

Handbook of Microprocessors, Microcomputers, and Minicomputers, John D. Lenk, Prentice-Hall, 1979

The Design of a Microprocessor-Based Data Logger, Kenneth J. Leap, Jr. and Lee A. Dedini, U.S. Geological Survey, Open-File Report 82-167

Onward With the COSMAC Elf!, Jeff Duntemann, Kilobaud magazine, February 1979

The COSMAC ELF is now reputed to be the fifth most popular microprocessor for hobbyists in the USA. The ELF has 256 bytes of RAM, a hex keyboard and two seven segment LEDs. A fundamental problem with trying to expand memory on the ELF is that the CDP 1802 IC has only eight memory address pins. To address more than 28 bytes requires the use of memory address multiplexing. This article explains the techniques needed to address up to 64k of memory.
(v3n6, july/aug 79)

I've scanned several articles from 1970's-era issues of RCA Engineer magazine. You can see the scans here.

From RCA Engineer v22n5, February/March 1977:

[RCA] Solid State Division's microprocessor business is built around the CDP1802 microprocessor, a CMOS implementation of Joe Weisbecker's COSMAC architecture, which is radically different from the Intel and Motorola architectures. COSMAC was specifically developed to minimize logic complexity, allow very compact programs, and interface efficiently with the outside world. This lower complexity permits us to manufacture the CDP1802 in CMOS at a cost comparable to NMOS and PMOS competition with its more complicated logic. And Solid State Division is able to compensate for its late start in this business by capitalizing on the well-known electrical benefits of CMOS technology - low and flexible power requirements, unexcelled noise immunity, and tolerance to wide temperature extremes.

The following two pages of CDP 1802 microprocessor data sheets are taken from CMOS 1800-Series LSI Product Selection Guide (MPG-180D) from RCA Solid State.

CDP 1802
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CDP 1802
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The following are news releases regarding software and development capabilities related to the 1802.

From QST magazine, April 2017, p87:

Ulrich Rohde, N1UL, recognized for pioneering work on SDR

While working under a U.S. Department of Defense contract at RCA in 1982, Rohde's department developed the first Software Defined Radio, which used the COSMAC (Complementary Symmetry Monolithic Array Computer) chip. Introduced by RCA in early 1976, the RCA CDP1802 eight-bit CMOS microprocessor - a 40-pin LSI integrated circuit chip - was the company's first single-chip microprocessor. Rohde was among the first to present publicly on this topic with his February 1984 talk, "Digital HF Radio: A Sampling of Techniques" at the Third International Conference on HF Communication Systems and Techniques in London.

From UK magazine Microprocessors, volume 1 number 2, December 1976:

RCA Solid State Europe entered the microprocessor market early in 1975 with the announcement of COSMAC, initially conceived as a two-chip general-purpose computing element aimed at inexpensive digital systems. The 8-bit microprocessor architecture is designed to give great flexibility, simplicity of programming and inexpensive interfacing, while the instruction set and input/output interface are designed to minimize memory requirements and system complexity. The microprocessor uses complementary MOS technology, characterized by very low power consumption, high noise immunity and tolerance to supply-voltage variations.

In November 1975, RCA announced the full commercial availability of a microprocessor family, encompassing the existing COSMAC (then designated CDP1801, but now replaced by the single-chip CDP1802).

A recent development from RCA Solid State, the CDP1802 is a logical extension of the earlier products. Essentially using the same architecture as the initial COSMAC device, it is a single-chip microprocessor using self-aligned silicon-gate C-MOS technology. The CDP1802 is accompanied by a series of peripheral and interface circuits, including ROMs and RAMs using silicon-gate and silicon-on-sapphire technology, plus input and output circuits.

The main features of the CDP1802 architecture are: simple architecture for ease of understanding by the user; the concept of separating addresses from instructions placing them instead into an array of internal registers and thus allowing many compact one-byte instructions; powerful built-in interface capabilities.

From UK magazine Microprocessors:

The CDS II development system for CDP1802 microprocessors includes a 19in rack-mountable chassis with printed-circuit backplane, internal power supplies, clock and controls, a front panel with controls and display, and seven plug-in printed-circuit modules including a central processor, control, address-latch and bank-select, RAM and ROM memories, I/O decode, and terminal interface. Seven spare memory module positions and ten spare I/O positions are provided. Extra memory or I/O modules are available as options.

The CDS II comes with both papertape and magnetic-tape cassette versions of the resident editor and assembler programs which can be loaded into the 4 kbytes RAM supplied. A floppy disc option is also available. The utility program provided allows the user to inspect and modify memory and to start program execution at any location. It can also load programs, dump memory, and interface terminals for serial ASCII data terminals. It automatically adjusts to baud rates between 110 and 1200 operates in full or half duplex mode (RCA Solid State Limited, Sunbury-on-Thames, Middx, UK. Telephone Sunbury-on-Thames 85511).

From UK magazine Microprocessors and Microsystems:

RCA's 1802 8-bit CMOS microprocessor is to be supported by the Tektronix 8001/8002A microprocessor development lab. Because of its CMOS characteristics, the 1802 is widely used in severe environments and/or portable applications.

From UK magazine Microprocessors and Microsystems:

A resident utility program for RCA's 1802 microprocessor has been developed by the Golden River Company. The program, GRUTIL, will provide 1802 users with the capability to load a program from an external source such as a Teletype keyboard, paper tape or a timesharing system. The program runs directly on Golden River's GR0430 low power SBC and on the MK4 control system.

By using one of four specified commands the user may interrogate memory and punch a reloadable paper tape, enter data into memory or load a program, transfer blocks of memory from one location to another or proceed with program execution. GRUTIL will detect bad syntax and data errors and allow the aborting of wrong commands. The output may be terminated at any time by the user.

The program is available in ROM or PROM and can be contained in a 1k chip. Program size is less than 1024 bytes of CDP 1802 machine code. Input may be either Teletype and paper tape or magnetic tape and cassettes. Suitable terminations include ASR33, TI733, TI 743 and VDUs at speeds between 10 and 960 cps.
(Golden River Co. Ltd., Telford Road, Bicester, Oxon, OX6 0UL, UK. Tel: Bicester 44551)

From UK magazine Microprocessors and Microsystems:

Two software packages support the COSMAC CDP1800 microprocessor family. Both systems, the RAL-II Level-II assembly language and the C-MAC macroassembler, are designed to cut development time. The RAL-II assembler, provided with the RCA's floppy-disk system, allows the assembly of COSMAC Level-II assembly language. Use of RAL-II shortens source code by about 35%, with the use of a class of special 'super-instructions'.

Also available with the floppy-disc system is the C-MAC macro-assembler, which has macroinstruction definition, conditional assembly and 'program-build'.

A range of fixed-point and floating-point binary arithmetic subroutines has also been made available. Among the packages is an implementation of the fixed-point subroutine on a 1 kbyte ROM. The software includes 31 subroutines including register save and mathematical companion operations, with arithmetic functions, format conversion and utility subroutines. The roujtines are all in 16-bit 2's-complement format.
(RCA Limited/Solid State Europe, Sunbury-on-Thames, Middlesex, Englanhd. Tel: Sunbury-on-Thames 85511. Telex: 24246).

From UK magazine Microprocessors and Microsystems:

A software package from RCA allows software development for 1802 microprocessor family to be carried out on the Intel MDS prototyping systems. This crossassembler consists of a macro file designed to run in conjunction with the Intel 8080/8085 macroassembler.

The crossassembler is designed so that the user writes his program in 1802 mnemonics, uses an MDS command to generate a suitable macrofile, and then assembles his program in the normal way to generate 1802 machine code.

For program loading into the 1802-based prototype, the user can use either an Intel EPROM programmer to develop the necessary firmware or the RCA transcoding program to load the RAM of an RCA Micromonitor, which can then be used for subsequent debugging.
(RCA Limited/Solid State Europe, Sunbury-on-Thames, Middlesex, England. Tel: Sunbury-on-Thames 85511. Telex: 24246).

From UK magazine Microprocessors and Microsystems, Volume 1 Number 6, August 1977:

RCA have just signed an agreement with Solid State Scientific Incorporated of Montgomeryville, USA, which will provide the company with artwork and tooling for the manufacture of the CDP 1802 8-bit CMOS CPU, the CDP 1822S 1-kbit silicon-on-sapphire RAM, the CDP 1824 256-bit RAM, the CDP 1831 4-kbit ROM, and the CDP 1852 8-bit I/O port.

SSS have been a large supplier of CMOS integrated circuits in the US since 1971 and will provide a viable second-source for these devices.

From UK magazine Microprocessors and Microsystems, Volume 5 Number 1, January/February 1981:

True full-screen editing on an integral data terminal with CRT display is featured in the COSMAC microprocessor development system, CDP18S008, from RCA Solid State for microprocessor systems based on the RCA CDP1802 and CDP 1804/5 microprocessors. The development system comprises VDU and data terminal with an ASCII keyboard with 72 standard keys and 14 special function keys; a dual floppy disc drive; 60 kbyte of user-accessible static CMOS RAM; a CDOS disc file-management and operating system; a new resident ASM8 macroassembler, editor and utility program on floppy; a plugin MOPS-augmented Micro-monitor (in-circuit emulator) for extensive online and offline debugging of both software and hardware; a builtin PROM programmer; and a builtin printer interface for RCA's new matrix high speed printer, CDP 18S050.

In single quantities, the RCA COSMAC Development System IV CDP 18S008 is priced at £s;7965.
(RCA Solid State Europe, Sunbury-on-Thames, Middlesex, TW16 7HW, UK. Tel: Sunbury-on-Thames 85511).

Microtutor The Microtutor, introduced in 1976, came in a custom box and was made up of the main circuit board, two plug-in boards, an AC power adapter and two manuals.

The manuals in this particular box are actually the same core text, just different covers and title pages. This COSMAC Microtutor Manual was written by J. A. Weisbecker at RCA Laboratories in Princeton, New Jersey and has the following Foreward:

Computers can be large, complicated, expensive, and hard to understand. MICROTUTOR is a computer that is small, simple, inexpensive, and easy to understand. It comprises 256 words of memory, input switches, a two-digit output display, and the RCA COSMAC microprocessor.

Contrary to popular belief, computers are quite simple in concept and fun to play with. They can be useful but we'll try not to dwell on this aspect in deference to more sensitive readers. A word of caution, if MICROTUTOR makes computers seem simple to you, don't tell anyone. You can earn more money perpetuating the computer complexity myth.

Readers who insist on knowing every last little detail about COSMAC should refer to the RCA COSMAC MICROPROCESSOR MANUAL. Readers who want to be protected from actual computer hardware by software aids with names like assembler, interpreter, simulator, and compiler should save up their money for a more expensive system.

Main Board The main board contains the "user interface" equipment, including eight input toggle switches, a Load (LD) switch and pushbuttons for Input (IN), Clear (CL) and Start/Step (ST).

The output is a pair of hexadecimal LED displays.

The main board also contains three sockets, for a Memory Card (M), COSMAC Card (P), and an External Option (E).

CPU card The plug-in COSMAC CPU card contains the two integrated circuits that make up the 1801 processor, introduced in 1975.

The chip on the left is a CDP 1801 CRD ("Microprocessor Register") and provides the Arithmetic Logic Unit (ALU) functions.

The chip on the right is a CDP 1801 CUD ("Microprocessor Control") and provides control and sequencing functions. It supports 59 op codes.

The subsequent CDP1802, introduced in 1976, combined the functionality of these two chips into a single deivce, as well as adding instructions.

Memory Card The plug-in memory card provides 256 bytes of Random Access Memory (RAM).

Click here for an in-depth magazine article on the Microtutor from 1976.

Microtutor II The RCA Microtutor II (CDP18S012), introduced in 1977, is similar to the more common COSMAC Elf. Programs are entered via toggle switches and a two-digit LED display serves as the output device. The Microtutor has a pair of expansion connectors (RCA refers to these as External Option Sockets), into which optional boards can be inserted.

Eight switches along the bottom allow direct entry of a hexadecimal value. A pushbutton switch IN enters the value. Three more switches provide MP (Memory Protect), LD (Load) and RN (Run) functions.

Microtutor II Microtutor II
Microtutor II The CDP1802CD microprocessor with what looks like a date code from 1977.
Microtutor II This is a 256 byte (yes, byte) RAM expansion card.

The following announcement appeared in the May-June 1978 issue of Creative Computing magazine:


Intended especially for engineers, students, and hobbyists who wish to understand and use microprocessors, RCA Solid State's COSMAC Microtutor II, CDP18S012, is a complete basic microcomputer system available for quick and easy hands-on operating and programming experience. The new RCA COSMAC Microtutor II, preassembled and containing its own regulated power supply, is based on the RCA CDP1802 CMOS 8-bit microprocessor and supersedes the original Microtutor CDP18S011. The new CDP18S012 provides input via eight binary toggle switches and output on two seven-segment LED hexadecimal digit displays plus a Q LED output. Additional toggle switches are provided for all the required controls to examine and alter memory locations and to initiate program execution. Microtutor II is provided with 256 bytes of CMOS RAM on a memory card which attaches to the base through a standard 44-pin connector. Microtutor II has a crystal clock for stabilized timing applications and a memory protect switch which inhibits the memory write operation to prevent an improperly running program from writing into itself. $195.

For further information and copies of the Product Description PD9: RCA Solid State Division, Box 3200, Somerville, NJ 08876, or from RCA Solid State distributors.

COSMAC VIP The COSMAC VIP (Video Interface Processor) has 1024 bytes of RAM, a hex keypad, a cassette interface for storing and retrieving programs, and a video interface. A 512-byte ROM holds an "operating system" (a monitor program).


Super ELF
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  Super ELF
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Super ELF
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  Super ELF
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You can see more photos by clicking here.

RCA COSMAC Microterminal
From 1977:
The RCA COSMAC Microterminal CDP18S021 is a portable data terminal designed to operate with the CDP18S020 Evaluation Kit or with comparable user-designed RCA 1800 series microprocessor systems. The Microterminal is a low-power, low-cost, small-size, non-hard-copy alternative to conventional teletypewriter or similar terminals.

Click here for a PDF of the RCA COSMAC Microterminal.

Netronics in Connecticut also offered a COSMAC system.

Netronics ELF II

This advertisement is from the May-June 1978 issue of Creative Computing magazine.

COSMAC ad May/June 1978
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Infocel The 1802 also shows up in some unexpected places, like this battery-powered hand-held unit.

Click here for more information and photos.

Click here for a 1974 article discussing the use of the COSMAC microprocessor in a system with communications links, floppy disks, and a television display.

CPU Selections
MicroprocessorMax. Clock Freq.Operating Voltage
CDP1802C 2.5 MHz ( 5V) 4 - 6.5V
CDP1802 5.0 MHz (10V) 4 - 10.5V
CDP1802AC 3.2 MHz ( 5V) 4 - 6.5V
CDP1802A 6.4 MHz (10V) 4 - 10.5V
CDP1802BC 5.0 MHz ( 5V) 4 - 6.5V

Type Nomenclature
CD 4-6.5V, ceramic package
CE 4-6.5V, plastic package
D 4-10.5V, ceramic package
E 4-10.5V, plastic package
CH 4-6.5V, chips
CW 4-6.5V, chips in wafer form

1800-Series Chip Identification

The following information is taken from CMOS 1800-Series LSI Product Selection Guide (MPG-180D) from RCA Solid State.

Part NumberDescription
Microprocessors and Microcomputers
CDP1802 Microprocessor
CDP1802A Microprocessor
CDP1802B Microprocessor
CDP1804A Microprocessor
CDP1805 Microprocessor
CDP1806 Microprocessor
CD4036A 4x8 RAM
CD4039A 4x8 RAM
CD40061 256x1 RAM
CD40061A 256x1 RAM
CD40114B 16x4 RAM
CDP1821 1Kx1 RAM
CDP1822 256x4 RAM
MWS5101 256x4 RAM
MWS5101A 256x4 RAM
CDP1823 128x8 RAM
CDP1824 32x8 RAM
CDP1825 1Kx4 RAM
MWS5114 1Kx4 RAM
MWS5114A 1Kx4 RAM
ROM's and EPROM's
CDP1831 Mask-programmable ROM 512x8
CDP1832 Mask-programmable ROM 512x8
CDP1833 Mask-programmable ROM 1Kx8
CDP1834 Mask-programmable ROM 1Kx8
CDP1835 Mask-programmable ROM 2Kx8
CDP18U42 UV EPROM, 256x8
CDPR512 Firmware ROM
CDPR522 Firmware ROM (Microterminal Controller)
CDPR582 Firmware ROM (Fixed-Point Binary Arithmetic Subroutines)
Input/Output Circuits
CDP1851 Programmable I/O (PIO)
CDP1852 Byte I/O - 8-bit I/O port
CDP1853 Decoder - 1 of 8
CDP1855 Multipy/Divide Unit (MDU)
CDP1856 Buffer - 4-bit
CDP1857 Buffer - 4-bit
CDP1858 Latch/Decoder - 4-bit
CDP1859 Latch/Decoder - 4-bit
CDP1866 Latch/Decoder - 4-bit
CDP1867 Latch/Decoder - 4-bit
CDP1868 Latch/Decoder - 4-bit
CDP1871A Keyboard Encoder, ASCII/Hex
CDP1872 High-Speed Input Port - 8-bit
CDP1873 High-Speed Decoder - 1 of 8
CDP1874 High-Speed Input Port - 8-bit
CDP1875 High-Speed Output Port
CDP1877 Programmable Interrupt Controller
Timer Functions
CDP1863 Programmable Frequency Generator
CDP1878 Dual-Counter Timer
CDP1879 Real Time Clock
Video Control
CDP1861 Video Display, Controller (VDC) ["Pixie"]
CDP1862 Color Generator Circuit
CDP1864 PAL Video Display Controller (VDC)
CDP1869 Video Interface System (VIS)
CDP1870 Video Interface System (VIS)
CDP1876 Video Interface System (VIS)
CDP6402 Industry Standard UART
CDP6551 UART (with baud rate generator)


Fixed-Point Binary Arithmetic Subroutines are available in a single 1-kilobyte ROM, CDPR582CD (4 to 6.5 volt operation) or CDPR582D (4 to 10.5 volt operation). In addition to the binary arithmetic subroutines, the ROM contains the code for the Standard Call and Return Technique. The ROM contains its own address latch and is located in memory at hexadecimal locations C000 through C3FF.

The Binary Arithmetic Subroutine Package includes 31 subroutines. Fifteen of these are binary arithmetic subroutines, fourteen are utility subroutines, and two are for format conversion.


From Reference 2:

Rapid annealing test results show that the hardened RCA/Sandia 1802 Bulk CMOS Microprocessor will function immediately after application of intense ionizing radiation pulses.

The successful fabrication of Megarad-hard Bulk CMOS Microprocessor in a joint effort between RCA and Sandia National Labs has recently been reported (Reference 1). This device is functionally equivalent to the commercially available RCA CDP 1802 COSMAC Microprocessor. It uses a polysilicon gate C2L (closed CMOS logic) CMOS process. The hardened 1802 microprocessor has been demonstrated to perform adequately after exposure to high radiation levels. It exhibits total dose hardness, neutron hardness, high logic upset level and excellent burn-out/latch-up immunity.

  1. A Radiation-Hardened Bulk Si-Gate Microprocessor Family, R.E. Stricker, A.G.F. Dingwall, S. Cohen, J.R. Adams, and W.C. Slemmer
    IEEE Conference on Nuclear and Space Radiation Effects,
    Santa Cruz, CA, July 17-20, 1979

  2. Rapid Annealing Response of the Hardened 1802 Bulk CMOS Microprocessor, John Scarpulla, Robert Mozulay, Christine Ausnit, Edward W. Hogan, and Richard H. Casey
    IEEE Transactions on Nuclear Science, Vol. NS-27, No. 6, December 1980

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