ROM Emulation

[Switch]

I have been asked to look at a project, he has an old car ECU and want to make the program data easy to change.

I suggested that we put the code into some flash memory and then alter it from there, the old rom is a 27C128 so its quite small in todays world.

I am not thinking that maybe I could simply put it all inside a PIC and emulate the ROM from there.

Anyone seen any other projects like this or have ideas how to emulate a ROM ?

[locko]

14 bit address bus....
8 bit data bus...
2 bit chip and output enable.....

Lots of pins already, but it could be done. You would need to monitor the OE and CE pins and then read the address and put the appropriate byte on the data bus.
It might be easier to write or find some software to change the settings you are interested in and then write back to the rom. It is fairly easy to make a simple programmer for these devices.

Do you know where the data you want to change resides on the rom, which addresses? You could use a pic to program just those addresses with the new bytes you need.


Paul

[Acetronics2]

Hi,

I'm not really sure ... BUT

something like this was done by the Honda Civic enthusiasts. But they change the EPROMS manually ...

Now ... something also has been done with PICs and RS 232 ... But the Pic ( a 16F88 ) is using the tables " for himself ".

I do not think a Pic will compete with 27C access times ... do you ???

let's think to a Pic loading 1/4 of a 27C512 ... with engine compulsory OFF ( remember : the bus must be shared between PIC and ECU !!! )

My point of view : an idea to forget quickly !!!

Alain

[locko]

Hi,

I'm not really sure ... BUT

something like this was done by the Honda Civic enthusiasts. But they change the EPROMS manually ...

Now ... something also has been done with PICs and RS 232 ... But the Pic ( a 16F88 ) is using the tables " for himself ".

I do not think a Pic will compete with 27C access times ... do you ???

let's think to a Pic loading 1/4 of a 27C512 ... with engine compulsory OFF ( remember : the bus must be shared between PIC and ECU !!! )

My point of view : an idea to forget quickly !!!

Alain

You are right about the access times of the chips Vs a pic, somewhere in the 90 to 120ns depending on manufacturer but I dont know fast the ECU will read off the data, I doubt it will be running as fast as the 12C is capable. But I've never played with ECUs so what do I know :) It may just read the wrong data because the pic is not fast enough and move on to the next address. That's why I think changing the rom externally would be an easier way to go.
Without using any algorithms I can copy a 120ns 12C512 in about 11 seconds so writing to every address in a 12C128 should take less than 6 seconds, even quicker if you are only going to change a few addresses.

A quick search turned up this site

http://www.i-club.com/forums/vbarticles.php?do=article&articleid=4

I don't have the time to read through it but it may give you some better ideas of what other are doing.

Regards,

Paul