About the assembly - it is not hard at all to learn assembly, afterall it consist of simple instructions doing exactly one thing, for example "ADD A, B" obviously adds two registers,
in this case content of B is added to A, and the result of addition is stored back to A.
The hard part is to learn to recognise higher level code - how an algorithm is described with the help of a lot of small instructions. Todays 8-bit microcontrollers outperforms in many aspects the ones used in LH 2.4, but still the later has some unique features and was not chosen accidentally. After many hours poking with the code I can tell that LH 2.4 code is written in pure assembly language, not in C or some other hi-level language. Some of it's parts are heavily optimized, and Bosch engineers did the great work back then.
Anyway, if someone wants to know what 8051 (SAB 80C535 is an 8051 derivate) assembly looks like and wants to learn it this is the best online resource:
http://www.win.tue.nl/~aeb/comp/8051/set8051.html
The SAB 80C535/515 datasheet and user manual can be downloaded from here:
http://linuxfan.org/~ipdown/mybrick/jet/80x515_datasheet.pdf
http://linuxfan.org/~ipdown/mybrick/jet/80x515_user_manual.pdf
Datasheet describes electrical parameters, pinout, footprint and features,
while user manual describes how internal features works, and how to program the processor
peripherals
At ecuproject can be found 218 EZK and 950 disassembly listings, I have them now more
complete, but the posted ones are still very good.
At last, even if I have much passion in this subject, I don't have enough free time,
and besides disassembly and dividing what is code and what data, tracing the interconnected hardware, there is still the core of the software which is mainly unknown.
There are a whole lot of optimized functions that are doing calculations, which have to be studied and understood, after which the program flow and logic can be deduced.
I work on this just because I want to know how the damn thing works, so if someone wants
to help understanding disassembly - please do!