Mitsubishi ECU - OBD Command Code and Protocol

OBD Command
Since there is a mistake on my first post regarding of the protocol,  I've made some more research on that. Here is the result on how the ecu response to the command.

Based on Christia999 code, I found the OBD command code was setting at here (refer to picture 1 and picture 2 below)

Picture 1 (The OBD Command)

 

  Picture 2

If we look further on the code comment, the OBD code were divided into few table ranges to store the variable value. Here are the table range comments by Christia999:

	;******************************************************************
	;*
	;* OBD interface queries, commands
	;*
	;* Codes from $00 to $3d: Regular queries, return the value of the
	;* variables showed in obdTable located below,
	;* see each variable definition... First value in table
	;* correspond to obd query code $00, increases by 1
	;* for each table value
	;*
	;* Codes from $3e to $3f: Converted to $3d, see that obd code
	;*
	;* Codes from $40 to $c9: Returns what is stored in that ram address
	;*
	;* Codes from $ca to $ca:: Erase all fault codes and returns $00 if
	;* engine not rotating. If engine is rotating, all
	;* actuators/injector commands are reset and $ff
	;* is returned.
	;*
	;* Codes from $cb to $f0: Returns what is stored in that ram address
	;*
	;* Codes from $f1 to $fc: Injector/actuators commands, returns $ff if
	;* successfull
	;*
	;* $f1: Activate boost control solenoid
	;* $f2: Unused in code
	;* $f3: Activate egr solemoid
	;* $f4: Activate fuel pressure solenoid
	;* $f5: Activate purge solenoid
	;* $f6: Turn on fuel pump
	;* $f7: Disable injector #6 (inoperative in code)
	;* $f8: Disable injector #5 (inoperative in code)
	;* $f9: Disable injector #4
	;* $fa: Disable injector #3
	;* $fb: Disable injector #2
	;* $fc: Disable injector #1
	;*
	;* Codes from $f1 to $ff: Special queries
	;*
	;* $fd: Serial link test, returns $b5 (E931) or $b7 (E932)
	;* $fe: resistor strapping low word from t_strap3
	;* $ff: resistor strapping high word from t_strap3
	;*
	;******************************************************************

view raw OBDCodeTableValue hosted with ❤ by GitHub

So how does it work? Let say we want to get the RPM value from the ECU. So the command we should be use is 0x21 (based on Mitsubishi ECU command that I've posted before). Whenever we send 0x21 command, the ECU will look-up at the variable value of the table which can be refer at the picture below.

So it is prove that the function for RPM is correct where RPM function is y=31.25*x and x is a value response by ECU.

Communication Signal

As I've wrote before, the communication with the ECU can describe as below:

• Serial communications rate is 1953 baud, 8 bits, 1 stop bit, no parity, TTL. 
• Communication signal is "Inverted"
• Communication referral as 1 byte sent and 1 bytes receive

There are some people a little bit confuse including me about the multiplexing communication. Wikipedia explain that multiplexing (also known as muxing) is a method by which multiple analogue message signals or digital data streams are combined into one signal over a shared medium.

Multiplexing communication between ECU

Reference:

• E931/E932 source files with comments and symbols.
• Multiplexing on Wikipedia