Does anybody know the exact baud rate and RS-232 protocol configuration (ie, data bits, start stop bits) for a 95WRX type ECU ?

I'm thinking of knocking a little module together that will convert from the bizzare Subaru format to something that a Laptop will understand.

It would also be useful to know the messaging protocol between the ECU and a select monitor.

Cheers

Giles

 

Stephen Done does (he figured it all out with a scope!!!!) but has put so much effort into it, he may not want to just pass on all his hard work.......

From what I can remember, the port is nothing like a "normal" RS232 type port/protocol so you won't be able to connect it up with the right cable and a Term package, you'll need custom written software (I think).....

Matt

 

Stephen wasn't able to release the info to me when I asked him sadly. Wish I'd got in earlier when it was all on his page would be REALLY useful to me now, but back then I couldn't have contributed much.

 

As a sort of sideline job I do a bit of embedded systems programming using 8bit processors (8051, 6052 etc). I'm no electronics expert but I write the software for them. The idea is to be able to convert the Subaru protocol (I've read it's something like 1953.6bps with weird start and stop bits) and turn it into something useful like 2400bps 8 data bits, that a common laptop could then use.

I've done something similar converting a magnetic card reader to an RS-232 stream using an 8051 processor derivative (87C51).

 

The earlier MY Select monitor connector and baud rate etc are different to the later (more standardised one) that Stephen has done most of his work on.

There's some early MY info at http://lillith.sk.tsukuba.ac.jp/~kashima/car/index-e.html

 

Most laptops can work with 5V RS232 apparently so you don't need the transceiver, but you would want to put something on the transmit line from the laptop in case it does put out +/-12V. If not the MAX232 is very easy to work with.

It is more the protocol and baud rates along with the commands that foxes me.

 

Can't you figure out the baud rate with an oscilloscope? As baud rate=symbol rate=number of state transitions per second. If it's as low as suggested (<2400 baud) it's unlikely there will be multiple bits per state transition (e.g. QAM).

 

I'm not worried about the levels of the signals, that's the easy bit to sort out. What does worry me is that it's not a standard baud rate and could possibly not have standardised start/stop bits.

Looking back at some Windows code I wrote for logging RS-232 transmissions I'm not entirely convinced I can set the baud rate to an exact bps. I've got a feeling that I will be restricted to 1200, 2400, 4800, .... etc. I'll have a go at altering to an unusual baud rate and see what happens..

If I can't set exact baud rates then I can use an 8051 chip to read the data (at any baud rate) from the ECU and then chuck it out at a standardised baud rate to the PC and vice versa.

I may well have to dig out the digital oscilloscope to get a recording of some information being sent. The main problem is knowing what actual data is being sent if any.

 

The Windows APIs may not let you choose non-standard baud rates, but I should imagine the UART will do it if you know how to force it to. What you really need to start with is an HP (now Agilent) protocol analyser or similar.

 

Good idea Carl, I should have thought of that myself

Funnily enough we have an RS-232 protocol analyser at work although it's pretty old now !!

I'm sure they would let me borrow it for a while as it's rarely ever used these days.

Cheers

Giles

 

I don't think it matters how old -- RS-232 is a pretty old standard. One of the green-screen ones should do the trick.