[Diy_efi] checksums & others

[Adam Wade]

--- - <titkoscim at maffia.hu> wrote:

> I'm wondering how can I find RPM signal value in the
> memory, do I have to understand the whole code, or
> is there some other tricky way?

Different ECUs have a variety of ways of calculating
and using that data, and getting the ECU to stop
running the fuel injection and sending the data over a
serial port or something would be quite a trick.  If
the ECU was not pre-programmed to output this data in
some fashion, you'd be hard pressed to get it.  I
believe some vehicles with electronic automatic
transmissions use the EFI ECU's engine speed signal
for controlling the transmission, so that is one
option.  Some pre-OBD II vehicles could read such data
from a port in real-time, but each iteration was, I
believe, proprietary.  OBD II compliant ECUs can
always have their engine speed read in real-time
through the diagnostic connector.

> I'm not much interested in incoming data logging,
> but memory dumping itself, like on C=64 with an
> action replay, one could freeze, look at memory,
> then go on, freeze again, look at again, and
> it was possible to find where certain data is stored
> in the memory.

I think that unless you have a developer's pack for
the MCU in your ECU and could run that package in a
debug mode, you're unlikely to be able to achieve
something like that.  Why would it matter where the
data is stored in memory?  The only way to get that
data back out again is through the MCU itself (unless
you had a memory controller chip like in a PC, where
an OBD II "chip" could read from memory as necessary,
and I don't think that would be the optimal solution
to the problem of feeding out OBD II data).

> So, I'm not interested in sensor outputs, but memory
> addresses where the ecu stores these information...

I'm still not sure why, but your best bet might be to
disassemble the runtime code and flowchart it.  Then
you would have a complete listing of where the stack,
scratchpad data, and maps are located in the running
ECU.

Since cars are not my forté, I will happily accept any
corrections or additions to the above.  Thanks.

=====
| 82 Honda CX500 Turbo (Cassandra)  90 Kwak Zephyr 550 (Daphne) |
| "It was like an emergency ward after a great catastrophe; it  |
|   didn't matter what race or class the victims belonged to.   |
|  They were all given the same miracle drug, which was coffee. |
|   The catastrophe in this case, of course, was that the sun   |
|     had come up again."                    -Kurt Vonnegut     |
| M/C Fuel Inj. Hndbk. @ Amazon.com -  http://tinyurl.com/6o3ze |


		
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