RE: Slider with Checksum

You are forgetting to add 1

The inverse of 3B is C4 you then need to add one

You will also have to be carefully when it goes over 255 if the checksum is
only 1 byte

In finding the two's complement of a binary number, the bits are inverted,
or "flipped", by using the bitwise NOT operation; the value of 1 is then
added to the resulting value.

-----Original Message-----
From: commandfusion@googlegroups.com [mailto:commandfusion@googlegroups.com]
On Behalf Of stbluesrul
Sent: 12 February 2010 08:22
To: CommandFusion
Subject: Re: Slider with Checksum

For the string \x08\x22\x01\x00\x00\x10 the checksum is C5

It's the 2's complement of the sum of all the values (That's what the
manual says). Now the way I understand this, is that it is basically
the sum of
(08+22+01+00+00+10) = 3B
Then take the inverse of 3B which is C5

I have an excel spreadsheet that can calculate this. You can also do
this in the windows scientific calculator. I can email you
spreadsheet if you like.

Here are the steps in the windows scientific calculator:
1) Scientific mode
2) Set to Hex
3) Set to Byte
4) Add up 08+22+01+00+00+10
5) Should = 3B
6) To get the inverse simply click the "+/-" button and the output
should be C5

On Feb 11, 6:27 pm, Jarrod Bell <jar...@guilink.com> wrote:
> I believe this will be possible in an upcoming release that allows for
> math expressions within commands.
>
> Could you post how to mathematically calculate the checksum for the
> protocol above? Then I can ensure our math system (which is already
> working in our beta builds) will be able to do this.
>
> Jarrod
>
> On Feb 12, 12:00 pm, stbluesrul <paul.l.cra...@gmail.com> wrote:
>
> > Is it possible to use the slider with a hex command that requires a
> > checksum at the end of it?
>
> > This will be for direct volume on a TV.
>
> > Examples:
> > \x08\x22\x01\x00\x00\x00\x2B  - Volume to 0
> > \x08\x22\x01\x00\x00\x10\xC5 -  Volume to 10
> > \x08\x22\x01\x00\x00\x64\x71 -  Volume to 100
>
> > The sixth byte would be replaced with [sliderval].
> > Since that number will change to where ever the slider is moved to, it
> > is going need a different checksum for each different volume level.
> > The checksum is two's complement and is the seventh byte as shown.
> > Will this be possible?

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