[jaket]

Hi!

I have too problem with checksum in odometer Malagutii.
I need 10 450km.

eeprom 24AA01

[jaket]

Hi all!

I can change milage and checksum +/- 2-3km, but after change more then 2-3km odometer resets to 00000. Please tell how calculate checksum. I cant find algorithm or ways properly calculate checksum.

Thanks in advance.
BR
jaket

[rerouter]

As we have yet to hear from the op again, do you have the option of running the odometer up say 16 or more km with the original eeprom image, then dump again to compare, with that i would be willing to take a look at what it should be,

[jaket]

Ok.

I have few km value

in eeprom #00#01#02#03#04
00000 km = 01 00 00 00 00 - readed after reset odometer - because bad checksum
00002 km = 03 00 00 02 00 - in #00 = 03 and #04 = 00 is checksum
20614 km = 57 00 50 86 80 - in #00 = 57 and #04 = 80 is checksum in #02, #03 is km value 5086 hexadecimal = 20614 decimal
20616 km = 59 00 50 88 80 - and now I think it easy, but 20617 looks like this
20617 km = DA 00 50 89 00 - checksum in 00# = DA and #04 = 00 ???

[rerouter]

I can not find a clear and consise method but one way that may get your out of trouble,

Take the last byte of the odometer, use that value directly as decimal, then convert back to hex and add 1,

20617's checksum has had 0x80 added to it again, which is something i have yet to determine why,

as for #4, at a guess its 0x80 whenever the checksums first nibble has 2 bits set to 1,

for 10450, try 54 00 28 D2 80

[jaket]

And nothing. Odometer reset.
I can't drive more than 1km

20 618 value looks like this 5B 00 50 8A 80

20 619 = 5C 00 50 8B 80

20 609 = 52 00 50 81 80

[rerouter]

Hmm, 20618 tells me what i may have done wrong, it appears you add the letter at its value, (so 8A = 80+10, +1) which is making me think your dump for 20617 had a read error (extra 1 at the start makes a 5 into a D) if this is the case your check-sum should be

85 00 28 D2 00

if this does not work, try #4 as 0x80 but that check-sum seems to line up,

[jaket]

Not working

I have another value

100km = 65 00 00 64 00
255km = 00 00 00 FF 00

And another

256km = 82 00 01 00 80

[rerouter]

Ok, went digging again, its a sum type checksum, (I'm will admit i am learning this as i go), which means your checksum should be FB for 00 28 D2 00, or 7B for 00 28 D2 80,

To calculate it i am selecting the 4 nibbles (in batronix prog express) calculating the sum checksum, then using only the last byte +1, from all the examples you have given this matches,

[jaket]

Yes, yes now is ok! Great job. Big thanks!

working on 7B 00 28 D2 80