calculating checksum

[Boostmeister]

I'm new to programming, so I have a basic question.

If I want to modify a stock or other chip, how do I calculate the new checksum?

Thanks

 

[TurboDave]

Any chip editing (hex editors) software worth it's salt will do it for you.

The only thing you have to remember is to NOT include the chip's first two bytes when running the calculate function. That's where the check sum resides, and you don't want it included in it's own calculation.

 

[Boostmeister]

As a test, I loaded the stock BBJK program. I configured the editor to read from 0002H to FFFFH. The checksum it calculated was different than that in the chip. What am I doing wrong?

 

[Boostmeister]

OK, I figured it out. The editor was putting FF in bytes 00 and 01, thus the wrong checksum. I just load addresses 00 and 01 with zeros, run the checksum, then load 00 and 01 with the just calculated checksum and save.

Now to do some tinkering!!

 

[TurboDave]

Why is the editor changing the values in bytes 00 and 01???????

It shouldn't change anything unless you tell it to

The edtor I use for example: all I have to do is highlight bytes 02 through FFF, and click on the button to calculate check sum. Then I just change the values in bytes 00 and 01 to reflect that value (assuming it's changed).

 

[Boostmeister]

I think I know why. When I selected a range of addresses there was a fill function that would fill any unselected bytes with a number, in this case FF. I just got the programmer 2 weeks ago and am still learning (it's a Superpro Z).

Are there any better hex editors out there in internet land??

 

[TurboDave]

I personally prefer Hex Workshop: http://www.bpsoft.com/downloads/

The free downloads (3.11) run for a specified period of time, then if you want to keep it, you have to buy a licence (I think it was $25).

 

[Boostmeister]

I tried Hex Workshop today and liked it a lot. Thanks for the tip.