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BCM computer


padgett
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I have a lot of data on the ECM but almost none on the BCM (one that controls radio, HVAC, & CRT). Does anyone have any technical data on the BCM components (CPU, RAM, PROM) and programming ?<P>New Proms/Roms are not a problem & want to reprogram a bit (temp/oil in summary display, eliminate the lamp test every time I open the door, etc) but first need to know exactly what am dealing with. Is it just a retargetted ECM with 680x base ? (would be easiest means and looking at the kludge on the ALDL not be a surprise).<P>Have been involved in flight control computers for F-16 so doubt that this is difficult just like to work from documentation.

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More I think about it, would be nicer to replace odo on dash ('88) with three digits of oil pressure, space, three digits of temp. That would provide display I want on stock dash (was thinking about transplanting a '90-'91). Anyone else have suggestions ? Will need to find a loose BCM to experiment with - anyone have an extra for sale ? - but have PROM burning capability so should not be difficult once the map is figured out.<P>Do not want to re-invent the wheel though - has anyone reverse engineered the BCM before or have an engineering worksheet ? (ones for ECM list locations).

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I too have wondered about toying with the body PROM program to change the way some of the accesories work. Like making the "headlight recomended" light come on right away instead of a mile down the road. Adjusting the A/C settings to better work with 134A. Unlocking both doors the first time you hit the unlock remote botton. Maybe it could be programed to turn on the headlights with the wippers (required in Illinois). Or turning off the fog lamps during the day. <P>I know the basics of using a prom reader/programer and editing software it seems a bit out of my leage. <P>No one on the net seems too worried about the BCMs. I would figure the ECMs may ork simular.<P>A few interesting links: <A HREF="http://www.thirdgen.org/cgi-bin/messgboard/forumdisplay.cgi?action=topics&forum=DIY+PROM&number=10&DaysPrune=20&LastLogin=" TARGET=_blank>http://www.thirdgen.org/cgi-bin/messgboard/forumdisplay.cgi?action=topics&forum=DIY+PROM&number=10&DaysPrune=20&LastLogin=</A> <BR> <A HREF="http://www.cruzers.com/~ludis/c3xref.html" TARGET=_blank>http://www.cruzers.com/~ludis/c3xref.html</A> <BR> <A HREF="http://www.mindspring.com/~amattei/eprom.htm" TARGET=_blank>http://www.mindspring.com/~amattei/eprom.htm</A> <BR> <A HREF="http://pweb.de.uu.net/pr-meyer.h/index.htm" TARGET=_blank>http://pweb.de.uu.net/pr-meyer.h/index.htm</A> <BR> <A HREF="http://www.geocities.com/ecmguy.geo/tuning/do_tune.html" TARGET=_blank>http://www.geocities.com/ecmguy.geo/tuning/do_tune.html</A> <P>Hope that helps. Keep us posted.<P>Tom

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Guest kennyw

PADGETT,<BR>f-16? You work on f-16s computers and ask me where the clips are for the tape player cover??? I would settle for you fixing my dash lites and dash dimming. It is hard enough for this old dog to get on line much less know how it is done. You not only want to know how it is done but change it! I have to admire someone who can do this type of thing. My hats off to you.............ken

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Padgett, I've been meaning to Email you after some of your comments lately about reverse engineering this stuff... I just graduated with EE degree, but I haven't started work yet, so I've been chanelling my boredom into my Reatta. Currently I've been working on replacing the tape player in my '89 with a CD player. The plan was to have it seemlessly integrated so that the CRT controlled it and thought it was a tape player. <BR> So far, I can turn the volume up and down, change stations, etc, on the radio from my PC in the apartment, but the tape specific stuff was delayed by my broken tape player. I finally replaced the belt (first player took forever, once you have the hang of it the next 6 don't take very long though. smile.gif" border="0, so now I could start trapping some of the tape messages on the Entertainment and Comfort Bus to learn how to make a CD player that looks the same.<BR> However... I think I might change direction and reverse engineer the CRTC instead, so that I could have real CD player controls on the radio page. If I do manage to (all of the parts in the CRTC have Delco numbers rather than real manufacturer numbers, which is going to slow things down), It might lend some insight into the BCM as well.<BR> I'd be interested in what you know about the communications messaging format of the ECM/BCM data line, since it might be similar to what I'm trying to figure out on the E&C bus. Thus far I have timing specs on the hardware protocol, and can fake messages to do things on the bus, but I have very little figured out yet about what each bit in the message does.<BR> I'll probably go take apart a BCM tomorrow and see if it has many parts (CPU, ram, possibly bus interface circuitry) in common with the CRTC. I'd love to hear what progress you make otherwise, and if you need any pinouts or anything (I don't know if you have a service manual), let me know.<P><BR>BTW, why aren't there any Reatta pictures on your website? smile.gif" border="0<P>Mark A Finn<BR>Recent Electrical Engineer Grad, Iowa State University<BR>Employed by someone, soon, hopefully.

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Ken: first thing any crew dog looks for is the tech manual, particularly on a new a/c - usually there is a change notice that tells you that screw F is now reverse threaded and overtightening gestrippen zie unreachable nutplate. Besides there is no way that plastic GM uses is mil-spec though have seen some dashes that would give Mr. Rubik fits.<P>Hence knowing where/what the clips are has saved many an odd piece<P>BTW: who has the best price on an accumulator 25528382 ? "6 Tests" say mine is marginal but not in a hurry.<P>Tom: thanks for the leads - had been on the gm-ecm mailing list (my other 2-seater is a Fiero) but s/n ratio got too bad.<P>Mark: Main reason for slowdown is twofold:<BR>80 hr/wk day job that has me on the road most of the time (just back from DC, New Orleans tomorrow).<P>Also I need to find a spare CRT/BCM/ECM and rig a test bed (not that difficult, have most of the necessary items including a logic analyzer in the back garage but..(see paragraph above).<P>Also spending too much time on CADF but then this time of year in Florida, outside work is "before ninety".

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Hi Skip,<BR>The kid just got a degree in electrical engineering, he now has my first Reatta, and after only about 1 month he knows more about Reattas than I ever will. Especially the electronics and the brakes.<BR>Jim

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My CRTC cracking is going to be delayed by some real work on my sunroof. I haven't looked in a BCM yet, but when I do I'll let you know anything I find. I've heard rummors that while GM used 68xx procs in ECMs, they supposedly liked Intel parts in other areas. Anyone know anything about this?<P><BR>As far as changing the BCM programming goes, I thought of another thing I'd like to see changed, the photocell-to-dash-dimming delay. I don't like the fact that when I drive into a tunnel the dash lights don't dim for twenty seconds. I haven't really played with it at all, maybe I should just turn the lights off and turn them back on.<BR><p><BR>Mark

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ECMs are Motorola 680x based (think originally 6802 but later units use a 6809 license-built by Hitachi - the 68HC0x (have a *lot* of data at home including compete disassembly, PROM maps, and bin lists from a number of car lines.<P>Reatta uses the second generation of these, commonly known as "P4" which replaced the 160 baud serial data link (ALDL) with one of 8192 baud. <P>Reatta actually has a fairly standard ECM with a 27256 PROM and the normal ALDL. Where it differs from most GM cars is that plug in the ALDL socket by the parking brake marked "do not remove".<P>For example the Reatta has an attribute shared with the Tech-1 scan tool that was prohibited to aftermarket vendors: it can clear trouble codes. This is done by the BCM in its role as a scan tool (the diagnostic mode reached by simultaneously pressing "warm" and "off" on the climate scream.<P>Suspect the BCM is exactly the same platform as the ECM, just with the addition of the HVAC and Radio controls (suspect these are discrete outputs matching the steering wheel controls used by the Pontiac Bonneville in 1988-1991. Where other cars limited control to the radio, the Bonneville's also controlled the HVAC and HUD. "Mute" would be nice as would a "medium" a/c fan setting)

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There's already a mute available. Pressing both volume buttons will mute the radio, pressing them again will return it to previous volume. I do agree that a medium fan would be nice.<P><BR> If I remember the manual diagrams correctly, the HVAC is driven by the "programmer", a box full of vaccum solenoids, which is connected to the ECM/BCM data line. The CRT Controller (CRTC) is also on this bus, and I belive is actually responsible for the scan tool like interface.<P><BR> The radio and tape player (and factory cell phone, if quipped) are also controlled by the CRTC, via a multi-drop serial bus. The data is sent over this Entertainment and Comfort Bus via a 1 kiloHertz pwm stream. There are actually very few discrete outputs on the CRTC: 6 wires for touchscreen/button/LED/beeper data, a wake-up line, video data, Vsync and Hsync.<P><BR> As soon as I get a chance I'll dump a prom from both a BCM and the CRTC and put them somewhere that others can look at them.<p>[ 06-18-2001: Message edited by: markfinn ]

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