You are my hero haha! I have a factory schematic for M2.3.2, which was pretty helpful for my reverse engineering of M1.7, but it would appear that you got the original for M1.7! I am super happy to get a copy of this thing.
Good point about the M1.7 only having 4 coil driver circuits, so yes, you will need to use 3 of them to run a wasted spark setup.
Control of T501 is done directly from S600 via the "ZDG" line. It is the same way that M1.3 and most/all of the other M1.x DMEs worked for distributed engines. If you look at my schematic, you will see that R501 is not populated. That resistor connects the base of T501 to pin 16 of S600 ("ZDG"). In the case of the M42, the "ZDG" signal connects to the "NRS" pin (#1) of S500, which functions as the output enable and is what sets the precise dwell. You will want to remove R501 and install R502 when you do your conversion. I would need to go measure the value, but since you are going to obtain M42 M1.7 units, you can just take the parts I suppose.
Pins 6, 10, 11 & 13 of S500 are what selects the output to activate, and those are low-precision timing signals that activate well before and deactivate well after the end of the dwell period (controlled by S702 which is a port expander peripheral that S700 issues to commands to by treating it as a very high-address in external memory). I assume that S600, which is a totally custom ASIC, is used because pin 16 connects to dedicated circuitry that is intended to provide sufficient base current to a coil driver transistor.
Really, the addition of S500 was a hack by Bosch to extend the functionality of the 8051-based M1.x platform to a few more vehicles, undoubtedly to save money. It works well, so this is not to say that it was a bad solution. It still impresses me that they wrote good enough firmware to be able to run a 6 cylinder engine on an 8-bit core running at 1MHz. Granted, the main loop starts to have difficulty running table look-ups at an optimal rate as you get to higher RPMs, but it is still pretty cool what they accomplished.
One thing that I would really appreciate some help with is getting an idea of what the various pin-name acronyms mean. Obviously they are referring to technical terms in the German language, and internet-translations are not always useful.
- ZDG is easy enough, and I assume part of it is Zündwinkel, which would make sense for what that signal does.
The ones I am really interested in are "KS" and "LL" in the S400/450/470 ICs. Those chips have latching input ("E#" pins) that will remain high after a high input if the corresponding output drives a minimum amount of current. The MCU checks to see if the output lines are held high or not after issuing a control signal, and this is how the ECU can set a code for a bad idle control valve, fuel injector, etc...if the driver IC does not deliver a minimum current, it is assumed that either a wire or the device has gone to an open circuit. The KS and LL lines seem to work as some combination of a master chip-enable, and a selector for whether the minimum current level is low or high for the fault detection. Since you are obviously technical and fluent in German, I am hoping that you can have some ideas for what things mean so that we can understand the function of these ICs better!
Other chips that would be good to understand acronyms for are S550 and S600.
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I assume you already looked through here, but if not, this Dropbox account has a lot of stuff related to the M1.7.3 project I did. I broke open a lot of the custom Bosch chips and got high magnification images of the silicon dies on the expensive microscope I have access to at work lol.
https://www.dropbox.com/sh/70yvbe8f83ur78b/AABzCRBHXVAGbM8G_Zt4JMGNa?dl=0
