![[RCA/Chrysler SCC]](vcf9_cry1802_1.jpg)
This Web page last updated Nov 19 2024. I describe the RCA 1802 computer version of Chyysler's Spark Control
Computer, emissions controls for their automobiles of the mid-1970's. This is part of a number of 1802 Membership Card Web pages about
a particular modern 1802 COSMAC product, and about the RCA COSMAC in general.- Herb Johnson
![[RCA/Chrysler SCC]](vcf9_cry1802_0.jpg)
Here's an exerpt from a 1977 Deluxe Automotive Encyclopedia edited by William Toboldt, published by Lexicon Publications in Chicago. the section on Chyrsler's Lean Burn is typical of automotive general descriptions of the Lean Burn product. Automotive literature of the period described the system functionally, and the controller itself as a "computer" without details of its internal construction or operation; also the product itself began as an analog controller, then included RCA's digital controller later. Lean Burn was one of a number of ways automotive producers tried to meet the new and lower emission standards established in the mid-1970's, with the then-limited technology of the period and the engines developed prior. The US government (and other governments') emission restrictions responded to growing air pollution - smog the most visible - due to coal, oil and gasoline consumption. - Herb
EMISSION CONTROL: Chrysler introduced the Electronic "Lean Burn" system on its 400 cu; in., 4 Bbl. V-8 engine during the 1976 model year. For 1977, lean burn applications were expanded to include 440, 360 and 318 cu. in. engines. A specially calibrated carburetor is used in conjunction with electronic spark advance to provide a way for the engine to burn a lean air-fuel mixture. Lean burn engines operate at at an 18 to 1 air-fuel ratio.
The lean burn system utilizes seven sensors, and a spark control computer located next to the carburetor. The computer consists of two electronic printed circuit boards that monitor signals from sensors throughout the engine.
The computer makes thousands of calculations each minute. It analyzes the signals received and determines the exact moment of combustion. Then, it signals the electronic distributor when to fire the spark plugs.
Engines equipped with lean burn system require automatic transmission. Due to tighter emission standards for 1977, lean burn engines are equipped with catalytic converters.
Developers of the RCA COSMAC looked for products for their microcontroller, which was suited for hostile enviroments. Chrysler was looking for cheaper ways to reduce emissions in their cars to meet 1976 EPA standards. The COSMAC was sold as a "programmable logic device" where a one-chip change supported each car model and engine. The "Lean-Burn" system controlled sparkplug firing based on engine timing, throttle position, air temperature and other engine signals. The products were also described and labeled as "Spark Control Computer" or SCC.
This product is one of the earliest real-time, embedded microprocessor controllers in production. But Lean-Burn got a bad reputation because of reliablity. It was mounted on the air cleaner and suffered from heat, vibrations and resulting poor connections. Also, the nature of pollution controls is to reduce engine power in order to completely combust (burn) hydrocarbons. Many car owners and particularly car mechanics want to improve power and engine response
a Chrysler Spark Control System module. These were first produced in 1976 and were produced into the early 1980s. They came in a number of configurations for several Chrysler models, with one of two sets of electronics, digital/COSMAC and analog. As of 2024 I'm not aware of any labling or part numbering that designates which electonices are in which Chrysler module. Auto mechanics would not service the internals, they replaced the entire module if it is determined to have failed.
from a Chyrsler Lean-Burn description, a SCC functional diagram of digital control of ignition spark timing
analog and discrete component version of SCC Instead of digtal program decisions, the analog electronics compares analog signals and are adjusted per Chyrsler model to output analog signals to control the engine.
SCC board with RCA COSMAC 1802 marked 1845A This is a 1982 dated RCA chipset. The chips have "82XX" year and week codes, a common industry practice for ICs.
The RCA Engineer, was an RCA publication distributed to electronic developers for decades. In this october 1979 article by D.R."Don" Carley, "Microprocessors in automotive electronics" describes RCA's 1802 as used by Chyrsler. Issues of issues of RCA Engineer V25 #1 to #6, were scanned by students of Alex Magoun, at one time the curator of the RCA/Sarnoff Museum.
"A CMOS microcomputer: The most advanced CMOS microcomputer developed by RCA is the 1804 microcomputer. It is an 8-bit CMOS/SOS device that has a powerful instruction set, 2K bytres of ROM and 64 bytes of RAM. For most engine control systems, only two LSI circuits will be needed, the 1804 microcomputer and a custom I/O circuit....
"For most engine control systems it will be necessary to develop a special purpose interface circuit for added logic capability and to provide adequate real-itme response, and an interface to the various sensors and outputs. ... This technique, called Automatic Placement and Routing (APAR), is based on a large number of standar logic cells [in a single chip] that are placed and interconnected by a computer [during the design of the chip]."
"System examples: Microprocessor are now used in several production engine control systems. Figure 6 shows a block diagram of a system developed by Robert Bosch GmbH [company] used by [BMW]. This system controls both fuel injection and the ignition. It is based on the RCA 1802 microprocessor with standard program and read/write memories, and an APAR input/output chip designed jointly by RCA and Bosch. The precise amount of fuel and the correct spark timing are determined by the informnation received from the sensors."
"A second example is a system developed by Chrysler Corporation to control spark timing based on six different inputs. The system uses only four LSI parts: the 1802, a standard RAM and ROM, and a custom APAR chip. An interesting feature of this system is that it contains a small PROM that can handle 4, 6 and 8 cylinder applications as well as allowing for some change in engine control constants. The system is mounted in the air intake to the air cleaner under the hood."
There's a patent trail for the digital Lean-Burn system. searching for Chyrsler patents yieled patent US 4128900, "Programmable read only memory for electronic engine control", assigned to Chrysler. Here's an exerpt:
"The present invention relates to an improved electronic engine control system provided by microprocessor integrated circuit 20, program memory integrated circuit 22, and PROM 23. Microprocessor integrated circuit 20 is a conventional device (for example, RCA Corporation CDP 1802D microprocessor) which carries out calculations used in computing the delay of spark firing in relation to each pulse from pick-up coil assembly 12.
There's likely other RCA or Chyrsler patents that link RCA and the 1802 to "electronic engine control".
In Chrysler advertizing of the mid/late-1970's period, the Lean Burn "computer" was part of the description of features of a Chrysler year-model automobile. Performance, comfort, style, engine displacment, and the computer were all featured. Personal computers were still a rarity. The fact that some Lean-Burn modules were still analog electronics didn't matter. They were also controllers and made wired-in decisions: close enough to being a "computer brain" as well.
Chrysler's documents which describe or document the Lean-Burn system, consist of shop manuals and test equipment instructions; also movies (later videos) promoting and servicing the Lean-Burn. The "computer" is treated as a black box, and never opened. Keep in mind: there were both analog and digital versions of the product, tested the same way, and replaced as a unit. I'm not aware of any Chrysler Lean-Burn service literature that says "COSMAC 1802"; I've looked at several Chrysler service documents over the years, and references from non-Chrysler-produced documents.
At a later time I'll provide Chrysler documents here. 2024 Web links to descriptions are provided in the meantime.
Here's a Hemmings.com article about the history and use of the Lean-Burn system.
Auto mechanic and technican's descriptions of the Lean-Burn system, like this 2022 Lean-Burn discussion among mechanics, don't often describe microprocessors. Generally the Lean-Burn system is considered troublesome, whatever is in the box. A common comment is "I finally had to swap out the Lean Burn for a conventional Mopar electronic distributor, which solved the problem." Apparently, later electronics (or simply new-versus-old) either worked, or did not sacrifice performance to improve combustion and reduce emissions.
Why was the microprocessor ignored by automotive techs? First, nobody serviced the processor, it was dunked in epoxy! No automotive service-level person ever ever dealt with Lean Burn at the chip level. The modules were tested with voltmeters or with a custom and expensive Chyrsler tester. Second, Chrysler also produced analog-electronic versions of the SCC, before and after the COSMAC version, and both were serviced in the same black-box way.
In 2013 I interviewed Toni Robbi, a retired RCA COSMAC engineer, at The Sarnoff Collection museum. From my Tony Robbi interview transscription, here's an exerpt where Toni describes RCA work on the Lean-Burn COSMAC development. I've added clarifying comments in []'s. - Herb
[Robbi:] .. and the computer stuff was the most fun I had. [but] beside the FRED [1802 developement] kind of stuff, I did automotive stuff. Like for Chrysler we designed one of the first computer controlled, engine control systems. And they actually produced it for several years. From the lean-burn systems, made with cosmac VIP [an RCA COSMAC development product].
That was in the late 70's I believe, becuase the Clean Air Act had come along and emission controls had been put on the automakers. So there was an opportunity there that we took advantage of.
[Herb:] Did they produce their own COSMAC, or did they use an RCA chip?
No! no, they used the RCA COSMAC. In fact Chrysler was our biggest customer for two or three years. It gave us the volume we needed, to build, you know, to make the [COSMAC part] prices reasonable, for other people to use. Kept it alive longer than it otherwise would have been, because we had a volume customer.
Conducted by the Computer HIstory Museum, "RCA 1800 Microprocessor Family Oral History Panel", an interview with Dick Ahrons, Nick Kucharewski, Paul Russo, and Richard Sanquini, who have "broad experience in the RCA microprocessor family .. we all had careers at RCA"
Kucharewski: .... But along the same time frame we were productizing the 1802 and went to Chrysler with basically an approach that said hey we could do an 1802 based solution that will give you a lot more programmability, a lot more flexibility. You could actually program spark advance using the processor and an external ROM that kind of thing.
Sanquini: How many years did it take?
Kucharewski: It took less than two years.
On a Web museum site in 2024, curated by Jack Ward, I found this 2004 description of an oral history of RCA engineer Gerald Herzog
EARLY TRANSISTOR HISTORY AT RCA by Gerald B. Herzog
Not only was the 1802 microprocessor used in space applications, but I had a group at the [RCA] laboratory that won a contract at Chrysler to develop a microprocessor control for their lean-burn engine system. This was in the early days of trying to improve gasoline mileage. Both Texas Instruments and my group at RCA had the contract with Chrysler, but my group was the only one that was able to drive a car to Detroit with the [prototype] microprocessor engine control in place.
Copyright © 2024 Herb Johnson
