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From: risto@tuura.UUCP (Risto Lankinen)
Newsgroups: comp.music
Subject: Re: MIDI SysEx Checksums (esp. Casio equipment)
Message-ID: <820@tuura.UUCP>
Date: 30 Oct 90 08:49:45 GMT
References: <2077@aber-cs.UUCP>
Organization: Nokia Data Systems Oy
Lines: 27

cho@aber-cs.UUCP (C.H. Orgill) writes:


>I am trying to write an Editor-Librarian on the Macintosh for a newly
>acquired Casio VZ-1. Fine so far, but in the SysEx documentation Casio
>omit to mention how their 7-bit checksum is generated. I can only
>assume they allude to some commonly-known format for MIDI checksums.
>Unfortunately, since this is my first programming experience of MIDI,
>I do not know this format ! I can only report that it is not (the sum
>of all the data bytes indicated) modulo 128. All clues gratefully
>received !

Hi!

The Roland MT-32 uses a method such that on the receiving side, the string
*plus* the checksum character 0..127 are summed, after which the modulo 128
should be zero.  To calculate the character, one first calculates the sum
of the data string modulo 128, and uses 128-<that_result> as the checksum
character (to make the string & checksum eventually sum up to 128*k+0 at
the receiving side).  This may (or may not) work with Casio.

Terveisin: Risto Lankinen
-- 
Risto Lankinen / product specialist ***************************************
Nokia Data Systems, Technology Dept *  2                              2   *
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