Fast-20 transfer period factor.
JLOHMEYE at cosmpdaero.ftcollinsco.ncr.com
Tue Nov 21 15:02:00 PST 1995
Ernie Rael wrote:
>The scsi spec says:
> The transfer period factor times four is the value of the
> transfer period.
>Value is ns. For 20 mega-transfers/second the transfer period is 50ns.
>Which implies the transfer period factor is 12.5. But transfer period
>factor is an int.
>So, is there any special convention here?
Yes, there is. A transfer period factor of 12 means a transfer period of
50. From the SIP draft standard, revision 8:
"The transfer period factor times four is the value of the transfer period,
with one exception. A value of 12 (0Ch) denotes a transfer period of 50
nsec. This is to accommodate the fact that 50 is not evenly divisible by 4,
yet is a value that must be supported since it represents the maximum
allowable speed within the Fast-20 timings specified for the SCSI-3 parallel
John Lohmeyer E-Mail: john.lohmeyer at symbios.com
Symbios Logic Inc. Voice: 719-573-3362
1635 Aeroplaza Dr. Fax: 719-573-3037
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