Check Sum

[mildflame]

I have been playing around with EPROMS but I don't quite understand what a checksum is... can someone explain it to me?

[Retropin]

Been a while since ive programmed an Eprom, but isnt Checksum where it validates data delivered against data now on Eprom?

[mildflame]

all i know is when i read a rom it changes, i don't even know if its supposed to change

[MartyJ]

http://en.wikipedia.org/wiki/Checksum

A checksum is basically a mathmatical representation of the file prior to copying.  It is a known value and checks it after copying to ensure it is valid.

Basically the same as a MD5 hash for a file on your computer (virus programs use these all the time).

For example - run.exe (made up file - is hashed and it has a known static value).  If one part of the code is modified or even a space added, the hash will have changed and wont match

[mildflame]

http://en.wikipedia.org/wiki/Checksum

A checksum is basically a mathmatical representation of the file prior to copying.  It is a known value and checks it after copying to ensure it is valid.

Basically the same as a MD5 hash for a file on your computer (virus programs use these all the time).

For example - run.exe (made up file - is hashed and it has a known static value).  If one part of the code is modified or even a space added, the hash will have changed and wont match

That would make sence, however I read a new rom and it gave me a checksum but then i read the same rom without touching it and the checksum had changed, it just keeps changing!

[goodolddays]

http://en.wikipedia.org/wiki/Checksum

A checksum is basically a mathmatical representation of the file prior to copying.  It is a known value and checks it after copying to ensure it is valid.

Basically the same as a MD5 hash for a file on your computer (virus programs use these all the time).

For example - run.exe (made up file - is hashed and it has a known static value).  If one part of the code is modified or even a space added, the hash will have changed and wont match

That would make sence, however I read a new rom and it gave me a checksum but then i read the same rom without touching it and the checksum had changed, it just keeps changing!

I can't really remember but I think that is normal

[johnwartjr]

Sounds like a bad ROM. If the checksum changes every time you read it.

[studley67]

milldflames dad here john.these roms came from you.they should be good.but i think it is our reader or software playing up.we are using a cheap gs40 reccomended by homepin.any help using this pllatform would e helpfull.

[studley67]

i am under the belief that a eprom's checksum is unique to the info stored onto the rom.and should be able to corespond to a known checksum for that software.correct me if i am wrong.for eg. flash checksum for green roms should all be the same.

[studley67]

mitch was playing with the reader saturday.i still do not have a clue about reading/writting eproms.does anyone have a link to a tuturial on using this reader/writer?

[The pinballist formally known as Dean Morgan]

 

i am under the belief that a eprom's checksum is unique to the info stored onto the rom.and should be able to corespond to a known checksum for that software.correct me if i am wrong.for eg. flash checksum for green roms should all be the same.

Correct, checksum should be same and is unique.  Should not change if same program is being added. Checksum is shown so u know it has copied correctly.

[Skybeaux]

The checksum should never change like you've described.
It's either a bad rom or a cheap shit programmer

[studley67]

i think the later fits the bill,thanks ken

[johnwartjr]

I have a bad one get out every now and then, if one you got from me is bad I will of course replace it. Just let me know what it is!

See what happens with another EPROM, see if its checksum changes. If it stays the same every time, and this one keeps floating around, there's something wrong with the chip.

The checksum of my chips is always printed on the label, your reader should give the same checksum.

[mildflame]

[Sorry guys I have been having Internet Issues]
Yea, I would compare the check sum with the one on the chip and it'd just change everytime I read it, however it is more likely the reader playing up not the new chip. The reader has preset functions so that it reads in differant styles depending on the brand and type of chip, perhaps I had the wrong setting? (I don't think so) There is nothin I can do about it, for now