Feature Desc riptions
6- 12 Maxt or Atl as 10K III
When transferring data with DT clocking on the SCSI bus, a significantly improved
form of error checking, cyclic redundancy checking (CRC) is used instead of the
tradit ional par ity chec king. With CRC checking , the devic e s ending data gener ate s a
four - b yte C RC chara cter bas e d on t he co nt e n ts of the b yte s bei n g transf e rred. Th e
receiving device also generates a CRC character as it receives the bytes. At the end of
a data burst, the sending device transfers its CRC character and the receiving device
compares the sender's CRC with its own. If the two CRC characters match, then the
data burst tr a n s ferr e d wi thou t e rr or.
In ST mode, the Maxtor Atlas 10K III u ses the traditional parity ch ecking method to
ensure error free data transfers.
A new feature (also known as “phy sical layer integrity checking”) in Ultra160 and
Ultra320 SCSI interfaces is the capabi lity of the initiator and ta rget devices to execute
a test sequence of commands before customer operation begins to ensure that the
SCS I bus can support the desired transfer rate. If errors are found, the initiator ca n
negotiate different transfer parameters until a working configuration is found.
•Domain validation can detect configuration problems such as:
•Wide devices with a narrow bus segment between them
•DT devices connect through an ST expander
•Broken connections
It may also detect poor quality cables, marginal quality signals, and improper
termination.
Domain valida t ion is impl em ented usi ng st a ndar d S CSI commands and new ve r sions
of the WRITE BUFFER and READ BUFFER commands. The sequence of
commands used f or domain validation may vary fr om system to system. The selec tion
of commands used is entirely under control of host firmware and software.
Also known as “receiver equalization with filtering.”AAF is a closed- loop method of
improving received signal quality by amplifying the fundamen t al frequency of the
signal while filtering noise and other undesirable com-ponents. Devices implementing
AAF est ablish t he gain of its ampl ifiers by setting t he amplitude of the high-frequency
portion of the training pattern to be the same as the low-frequency portion at the
beginning of the training pattern. Using the training pattern to perform this
adjustment of signal amplitude provides for an inherent closed-loop system that can
adju st signal quality for differen t cable plants and chan ges in system c onditions (e.g.,
when a new device is added to a system causing the electrical characteristics of the
cable pla nt to change). AAF settings may be adjusted as often as necessa ry because
either the initiator or target may initiate the training pattern sequence. A receiver may
dis a b l e tra n s m i tter p r e- co m p e n s ati o n in a tra n s m i tter a s A A F p erforms bet te r i n th e
configuration.