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Old 09-27-2010, 05:45 PM   #41
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External boxes? I thought that one of the driving philosophies behind the whole MS3 project was to make a one-size-fits-most box that didn't require a lot of kludging to make work on the majority of modern engines?
That's right, and I feel that's what we've done. The majority of people run high-z injectors and +5v logic-level spark outs, so that's what we did. We felt that if the small minority needs another box to run their injectors or coils, that's not a big deal.

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The pretty pictures say things like "Good engine ground", however I can't find any discussion anywhere of which pins on which connector are which ground. Nothing tells me "The injector drivers go to ground through pins x, y and z of connector A, while the medium-current relay drivers go to ground through pins x and y of connector B. All analog grounds are isolated to pin x on connector C. A polyfuse conjoins ground planes X and Y at such-and-such point, and may be removed if you experience noise-coupling into the analog sensors."

I also see absolutely no mention of injector grounding on the "Fuel System" page, and no discussion of the underlying hardware in the "Ignition System" page. The one thing I do see here is that "for 99% of installs you should set Spark Output to "Going high (inverted)" with absolutely no discussion of what this actually means, or the fact that, in reality, the "Inverted" setting is NON INVERTED.
You don't see any mention of it b/c there doesn't need to be. The high-current (injector and medium current outputs) ground through the ms3x's db37, the analog and low-current stuff grounds back through the expansion connector down into the v3/3.57 board (which at this point shouldn't really have anything high current running from it anymore).

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In fact, I only just now realized something (Depending on how much "not like" the sequencer the MS3X isn't.) They could have avoided the need for any software foolishness in the bootloader (and achieved a properly Fail Safe configuration" by pulling those lines (between the CPU and the 74ACT541) weakly to ground rather than weakly to +5. The MC9S12 can source just as much IO current as it can sink, so that would have left the circuit "inverted" but prevented the outputs from going high when the CPU was not in control of them.
We pull those lines to ground instead of +5v.

The inverted vs non-inverted output terminology goes back to when the LED-style outputs were "normal" and connecting to VB921 or other IGBTs were "inverted." I've already discussed changing the naming there with James to make more sense.

Ken
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Old 09-27-2010, 06:15 PM   #42
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The one thing I do see here is that "for 99% of installs you should set Spark Output to "Going high (inverted)" with absolutely no discussion of what this actually means, or the fact that, in reality, the "Inverted" setting is NON INVERTED.
Before I melt a coil. For those of us running the improved spark circuit in a MS3 which setting should we be using?
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Old 09-27-2010, 06:40 PM   #43
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Before I melt a coil. For those of us running the improved spark circuit in a MS3 which setting should we be using?
If you are not using the MS3X, and instead wiring your ignition drivers off the outer LEDs on the 3.0 / 3.57 board, and you're using my "improved" (double-inverting) output driver, then you will set spark out to "Inverted" (which is non-inverted) just like you would with an MS1 or MS2.
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Old 09-27-2010, 06:59 PM   #44
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The inverted vs non-inverted output terminology goes back to when the LED-style outputs were "normal" and connecting to VB921 or other IGBTs were "inverted."
All grieving aside, I've honestly never understood the use of the terminology, even in this environment.

Going back to the VB921 design, a positive voltage applied to the "input" terminal of the 921 from the CPU causes the 921 to turn "on", which allows current to flow through the coil.

In such an environment, one must set "Spark Out Inverted" to "Yes."

Do you have any recollection of what the rationale behind that nomenclature was? To me, the word "inverted" would imply something other than the "normal" method of operation, which even back then was for the CPU to raise one of its output pins high when it wishes for the coil to operate. From the CPU's point of view, "high" = coil on, and "low" = coil off. And yet that is what got called "inverted".


In other words, my "improved" spark driver works precisely the same way as the very first ignition-capable Megasquirts did. And yet in both systems, "inverted" means that the ignition coil follows the state of the CPU output pin controlling it, rather than being inverse of it.


I've never understood why the nomenclature was written that way. It only makes sense if the "inverted" vs. "non-inverted" nomenclature wasn't coined until people started using the LED circuits to drive wasted-spark coils with on-board igniters, in which case (assuming the "standard" circuit) the "non-inverted" nomenclature makes sense, not from the point of view of the CPU, but from the point of view of the inverting output driver.

But as you said, the term supposedly predates this.
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Old 09-28-2010, 10:42 AM   #45
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Originally Posted by Joe Perez View Post
I've never understood why the nomenclature was written that way. It only makes sense if the "inverted" vs. "non-inverted" nomenclature wasn't coined until people started using the LED circuits to drive wasted-spark coils with on-board igniters, in which case (assuming the "standard" circuit) the "non-inverted" nomenclature makes sense, not from the point of view of the CPU, but from the point of view of the inverting output driver.

But as you said, the term supposedly predates this.
The very first attempts to drive an ignition with MegaSquirt used the FIDLE output to drive an external module (IIRC, it was a 4 pin HEI). They'd add a pull up resistor, so the circuit both worked as a buffer and inverted the output. The output of a pulled up FIDLE circuit is just like the LEDs. Then somebody tried using a different module - it may have been an MSD box or a Bosch 139. These two trigger off the opposite edge, so they started calling it inverted spark output. Later code versions started using the LED circuit, but it took a while before anyone started installing an IGBT inside the case and driving it directly from a processor port.

It is a bit strange that this same confusion carries over into MS2. The reason is a little different there - the original (pre-CANBUS) MS2 design had a small transistor on the spark output that was dropped from later versions.
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Old 09-28-2010, 02:44 PM   #46
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Joe, if you want to continue the schems discussion, I will happily do so on the phone. I am PMing you the number.

Ken
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Old 09-28-2010, 04:01 PM   #47
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shame, there are other readers on here following this topic with interest you know...
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Old 09-28-2010, 07:08 PM   #48
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If I could actually change the policy, then the "outcome" of any phone conversation would be useful to everyone... but since I can't, I'm not sure that it's useful.

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