IBM DCAS-32160 - Ultrastar 2.1 GB Hard Drive, Технические характеристики

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9.1.1 COMMAND COMPLETE (00)
The file sends this message to the initiator to indicate that the execution of a command has terminated and
that valid status has been sent to the initiator. After successfully sending this message, the file releases all bus
signals and goes to BUS F R E E phase.
9.1.2 SYNCHRONOUS DATA TRANSFER REQUEST (01,03,01H)
Byte Value Description
ÄÄÄÄ ÄÄÄÄÄ ÄÄÄÄÄÄÄÄÄÄÄ
0 01H Extended message
1 03H Extended message length
2 01H SYNCHRONOUS DATA TRANSFER REQUEST code
3 M Transfer period (M times 4 nanoseconds)
4 X REQ/ACK offset
Figure 123. Synchronous Data Transfer Request.
A pair of Synchronous Data Transfer Request (SDTR) messages shown in Figure 123 are exchanged
between an Initiator and a Target to establish the synchronous data transfer mode between the two devices.
The message exchange establishes the permissible transfer period and R E Q / A C K offset for a synchronous
data transfer between the two devices. The initiator may initiate a synchronous data transfer negotiation at
any time after the L U N has been identified.
A Synchronous Data Transfer Request(SDTR) message
exchange shall be initiated by an SCSI device whenever a previously arranged data transfer agreement may
have become invalid. The agreement becomes invalid after any condition which may leave the data transfer
agreement in an indeterminate state such as;
1. after a Power-on Reset
2. after a SCSI Bus "hard" reset condition
3. after a Bus Device Reset message
In addition, a SCSI device may initiate a S D T R message exchange whenever it is appropriate to negotiate a
new data transfer agreement(either synchronous or asynchronous).
M The transfer period(M above) is the minimum time allowed between leading edges of successive
R E Q pulses and of successive ACK pulses to meet the device requirements for successful recep-
tion of data. The file supports transfer period in the range 100 nSec to 475 nSec in 25 nSec incre-
ments.
REQ/ACK Offset
The A C K / R E Q offset(X above) is the maximum number of R E Q pulses allowed to be out-
standing before the leading edge of its corresponding ACK pulses is received at the file. A
R E Q / A C K offset value of zero indicate asynchronous data transfer mode. The file supports
R E Q / A C K offset values in the range 0 through 15.
If A T N is negated before all bytes of a multiple-byte extended message is received, the file will go to BUS
FREE to signal a catastrophic error.
9.1.2.1 Synchronous Negotiation Started by the Initiator
The Tareget responds to each Initiator requested transfer period as shown in the following figure Figure 124
on page 167:
166
O E M Spec. of DCAS-34330/32160