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CeC technical information?

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MIPS View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MIPS Quote  Post ReplyReply Direct Link To This Post Posted: Aug/21/2023 at 11:58am
The goal was that it helps deal with the two most common failures of the CEC:

-Blown output drivers due to wiring problems (I reverse engineered the chip pinout on the previous page, so now we know what to expect when replacing or substituting them.

-Failures associated to "bit rot" as the microcontroller ages. The chip selected by Ford and OEM'd to AMC allows you to select an external ROM and disable the internal ROM by pulling one pin.

Optionally, the Jeep crowd already has experience with the design of the Renix computers. 80's era AMC's are only now starting to gain interest with younger crowds, but there is no substantial amount of technical information to start with for when our computers develop faults. I'm hoping that by going as in-depth as I have I can provide a starting point for anyone else in the years following, rather than it remaining a mystery. That and I'm bored and need to do something to keep myself busy at times.

It does however open the door if someone wishes to completely reverse-engineer the code to substitute computers without alterations to the vehicle harness, since retrieving the firmware was one of if not the hardest part. This was mentioned a few pages back. That especially is far beyond my technical knowledge at this time.

Edited by MIPS - Aug/21/2023 at 12:12pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Sep/08/2023 at 2:16pm
Wow, you've really got a hand on this thing! So that's the entire ROM listing?

I wrote tons of Intel 8080, z80, 8086, 8051 (superset of the 48) and assembly language on a half dozen other micros and minis.

OK post edited. I read the whole thread again.

What's needed to decipher the code is a schematic of the board, so we can know what sensor is connected (eventually) to what pin on the MCU, and a general sense of what that signal does.

You have an amazing amount of information and state about what signals and what order, appears at the connector.

Code like this is I/O intensive -- lots of those instructions are fiddling with I/O pins.

It's been 30 years, but I wrote a lot of assembly language for most of the early (1970s) micros. I can't commit to taking on the rest of the disassembly (IDing, naming, commenting the code) but I'll gladly help.


Here's a readable and complete copy of the programmers manual for the MCS dev system and the chip(s), just FYI. The one on bitsavers is an OCR mess.




Edited by tomj - Sep/08/2023 at 3:00pm
1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Sep/08/2023 at 2:29pm
Originally posted by FSJunkie FSJunkie wrote:

...The ECU continuously monitors the knock sensor and the pulses from the ignition coil indicating a spark plug firing for a power stroke on a cylinder....The ECU performs this function for each cylinder individually so each cylinder runs at it's own unique optimum ignition timing. It has no idea which cylinder is number one.

It's genius.


I missed this 2019 post. 

That is genius, and accomplished with so little information. And in a processor to dumb to run a microwave oven (today).
1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Sep/08/2023 at 3:08pm
Originally posted by MIPS MIPS wrote:

The goal was that it helps deal with the two most common failures of the CEC:

-Blown output drivers due to wiring problems (I reverse engineered the chip pinout on the previous page, so now we know what to expect when replacing or substituting them.


I'd watch for blown commutating diodes, across the solenoids to absorb the inductive dump. Old diodes in this service die relatively often. I'd replace, or augment, with a modern Schottky diode, far more rugged than anything from the past. Cheap insurance. Something like this:

https://www.digikey.com/en/products/detail/vishay-general-semiconductor-diodes-division/SB1H100-E3-54/2146191


1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com

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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomj Quote  Post ReplyReply Direct Link To This Post Posted: Sep/08/2023 at 7:00pm
That odd-looking 40-pin DIP chip with the socket on the back, appears to be National Semiconductor NS87PC48D, a second-sourced 804x with external 2708 type EPROM socket on top.

https://en.wikipedia.org/wiki/Intel_MCS-48

A photo of one is at the bottom of this Wikipedia page; scroll to just above the very bottom.

1960 Rambler Super two-door wagon, OHV auto
1961 Roadster American, 195.6 OHV, T5
http://www.ramblerLore.com

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Post Options Post Options   Thanks (0) Thanks(0)   Quote MIPS Quote  Post ReplyReply Direct Link To This Post Posted: Sep/11/2023 at 8:58pm
Yeah looking back I did a trace-out of the 1982 computer's circuit board but no good front/back photos. The 1984 computer has front/back photos but no layout diagram.
One thing that I could try is pull the IC's and drop them into an "Identifier". they're kind of magic, they probably don't work great and if it's an IC not in its library it won't know what to think of it. On the other hand because it's all probably relabelled parts, as long as they are correct on my assumption of being conventional drivers and op-amps it might let out the last of the secrets.
Unfortunately as I'm sure people have noticed I'm a hardware person and have never programmed software in my life. The instruction reference is handy but it will take me quite a while to comment every line.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote billd Quote  Post ReplyReply Direct Link To This Post Posted: Sep/11/2023 at 10:50pm
My 82 wiring harness and ECU. Found it interesting what it interfaced with and what it did NOT interface with.....
My "coding" such as it was, was limited to VB Script, and programming Juniper and Cisco firewalls, switches and ASAs (routers)  


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Post Options Post Options   Thanks (0) Thanks(0)   Quote MIPS Quote  Post ReplyReply Direct Link To This Post Posted: Sep/13/2023 at 2:27pm
There's a considerable amount of confusion on the altitude jumper wire that I've seen. The TSM states it's only used (attached to ground) when you regularly drive above 4000 feet. It also states that you will often find this as a crimped eyelet that bolts to the block somewhere behind the distributor. Some models have the wire but it's tied back and not grounded (low altitude mode). In vehicles like mine there is no jumper, but you will find the eyelet with TWO wires crimped to it, but if you compare continuity from ground to the altitude test pin on the diagnostic connector it's open. There's a bulletin stating that for 82 vehicles you have to add an extra pin to the computer connector and run that to a grounded point to enable high-altitude, if your vehicle was not originally built for high-altitude. Alright so this thing has the jumper and it's reading open so whatever, delete it.
Yeah, no. I've yet to pull the computer out again (really it sucks to reach) but while one of the wires is a mystery to me and isn't listed in the TSM schematics or the CeC wiring diagram, you will notice the other wire on that eyelet is the ground for the computer. It can ground itself through other components of the system, but it was built to ground everything in the CeC harness through here. Remove that and expect to pull your hair out with computer issues, if the computer works at all.

The 1982 TSM lists the pinout for the connector and where it all goes. I might of posted that near the start of the thread. From the connector pinout you look at the circuit layout but at that point I've yet to link the traces to their respective IC's.

Edited: Page 2. It's on page 2.
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