Parity jumpers

John Lohmeyer John.Lohmeyer at
Tue Apr 29 15:09:20 PDT 1997

* From the SCSI Reflector (scsi at, posted by:
* John Lohmeyer <John.Lohmeyer at>
At 06:30 PM 4/24/97 +0200, Francesco Ceci wrote:
>* From the SCSI Reflector (scsi at, posted by:
>* Francesco Ceci <f.ceci at>
>I'd like to know what the Scsi specifications recommend about the parity
generation and checking.
>By experience, I know that all Scsi devices generate the parity, while the
parity checking is normally controlled by a jumper that allow to
enable-disable it.
>Is it true?
>I pose to you the question, because I've found that the new Yamaha CDR-400
cd-writer, when the parity jumper is off ( disabled ), doesn't generate the
parity during Data phase.
>Thanks in advance for any help you can give me.

SCSI-1 said:

  "Data parity DB(P) is odd.  The use of parity is a system option (i.e., a
system is configured so that all SCSI devices on a bus generate parity and
have parity detection enabled, or all SCSI devices have parity detection
disabled or not implemented).  Parity is not valid during the ARBITRATION

This is consistent with the convention you observed about the jumper
disabling detection, but generation always being enabled.

SCSI-2 and beyond require parity generation and detection (except during

So, if you will excuse the pun, the Yamaha CDR jumper is rather odd.  But
it is not in violation of any of these standards (if you have the jumper in
the correct setting).


John Lohmeyer                 E-Mail: john.lohmeyer at
Symbios Logic Inc.             Voice: 719-533-7560
4420 ArrowsWest Dr.              Fax: 719-533-7036
Colo Spgs, CO 80907-3444    SCSI BBS: 719-533-7950 300--28800 baud

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