Re: Checksum formats
Re: Checksum formats
- Subject: Re: Checksum formats
- From: Doug Wyatt <email@hidden>
- Date: Mon, 3 Jan 2005 10:00:59 -0800
On Dec 24, 2004, at 1:39, Peter Karlsson wrote:
Dear list!
This is maybe not a question for this list, sorry if that's the case.
I need information about different sysex checksum formats in
synthesizers.
Are there a complete list somewhere, or at least a collection of some
of
the variations used? I need this information to be able to implement
checksums functions in my multi device - library - editor app.
Generally there are two methods:
1. sum the bytes and AND the result with 0x7F
2. the two's complement of the above (can be implemented by starting
with 0 and subtracting each byte from the sum, then again ANDing the
final result with 0x7F)
Where things vary more substantially is how to determine which bytes in
the sysex message are checksummed. Generally the summed bytes might
always end right before the checksum byte itself, but where to start
varies by manufacturer and possibly model. You may find that Roland
devices are highly consistent but I'm not sure about that and I
definitely can't offer any more than that off the top of my head.
Doug
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