I really appreciate ur efforts and seems as if u worked passionately to resolve this issue. U r far ahead in ur findings, but I would go step by step so that if u missed anything anywhere, I would grab it 4 u. Thats professionals way of tackling to problems isn't it?
I do understand that y u ve used Max232 and offcourse we need to cater the difference in baud rates (as lowest possible in serial interface of a PC is 9600). However, RS-232 standard specifies voltage level of 'zero' from +3 to +15 volts and 'one' from -3 to -15 volts. Same has been verified by physically measuring on DB-9. So in my opinion we need to cater both baud & volts in our design. The cct diagram u pasted at the forum and some other ccts similar to it are available on the web and people claim that they do work with their vehicles. But we need to find or design the one that suits our ECM.
I ve critically analyzed the circuit u pasted & some others, since last week, and found it to be taking care of the baud/volts/signaling requirements of both ends. Only one doubt is there, and offcourse I m going to verify that doubt today InshAllah. Following r the findings of this week which I can proclaim confidently:-
a) Daewoo racer has ECM that runs a programm of pre-OBD-II standard.
b) It has GM-ALDL 12 pin (North American type) interface connector.
c) It transmit/receive through pin 'M' utilizing bidirectional but half duplex UART data comm.
d) The baud rate of this data comm is 8192 with 5 volts p-2-p, and the standard is known as GM XDE-5024B.
Looking forward for any amendment in said understanding from all brothers.
Khuda e Paman