Data Sheets


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
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

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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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
CDPR582 Firmware ROM
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)

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Updated August 24, 2016