Checksum correction using the math!!!

[jared_poe]

Hello to all, according to you ? can correct the checksum using only a mathematical calculation?
Let me explain, I took the file to a chroma edc16c39 (chk =89e5), a point on the map I added 1 to the new file I saved with the name "test 01 +1" (chk =89e6), on the same file in another point I removed 1, the new file I saved with the name "test 01 +1 -1" (chk =89e5) at this point, in theory, if riscrivessi the files in the ecu, not me should give no error, right?
If this ? true means that at the end of any editing just make the difference between the two chk and subtract (or add it) in the area of the chk to report the value of the chk as the original.
I keep the tests in the meantime, I'd like to hear your opinion on this topic

[jared_poe]

Pi? the tests I do more? I do not return to the accounts...someone can? explain to me what you refer to those values that I have marked red

[GPoint]

Very interesting, could be very useful in the case you do not have the driver that will automatically calculate the checksum and then ? doable the manual correction. But the area relative to the correction of the chksum how it is identified?

[jared_poe]

On some of those ? towards the end..***** s, I am continuing with the tests...no ? cos? as simple as I thought

[GPoint]

That difficulty? you've found? Changing pi? bit the speech is pi? compplesso?

[jared_poe]

Exactly, also I still don't understand what are those values that I have highlighted in the picture

[ugoboss]

there are cks 8-bit and cks 16-bit and 16-bit are not easy to fix by hand , then you need to know c? The rsa and it gets more and more difficult, then there are various areas of cks, doesn't it ? that you can go to correct where you want, I say unto you, that in the end ? almost impossible in the ecu of the latest generation.

p.s. why you want to complicate things for your life when there are the sw that can help you.

[jared_poe]

Could be useful in case you do not have the driver..***** s, thank you for the info, cos'? the' RSA?

[sergiot]

your assumption that with the +1 and -1 in different locations was valid on many units up until 1995, 2000, when they used the eprom or the like.
with the introduction of the flash have adopted different systems and your calculation ? pi? valid.

[rickymix]

hi

can you expain it

I'm intressed for it please

i like to learn