Synchronous Data Transfer Request (01, 03, 01H); Table 168. Synchronous Data Transfer Request - Hitachi HUS151473VL3800 - Ultrastar 73.4 GB Hard Drive Specifications

19.1.2 Synchronous Data Transfer Request (01, 03, 01h)

Table 168:
Synchronous Data Transfer Request.
Byte Value Description
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
A pair of Synchronous Data Transfer Request (SDTR) messages shown in Figure 159 are exchanged between an Initiator and
a Target to establish the synchronous data transfer mode between the two devices. The message exchange establishes the per-
missible transfer period and REQ/ACK offset for a synchronous data transfer between the two devices. The Initiator may ini-
tiate a synchronous data transfer negotiation at any time after the LUN has been identified. A SDTR message exchange shall
be initiated by a SCSI device whenever a previously arranged data transfer agreement may have become invalid. The agree-
ment becomes invalid after any condition that 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 Target Reset message
In addition a SCSI device may initiate a SDTR message exchange whenever it is appropriate to negotiate a new data transfer
agreement (either synchronous or asynchronous).
M The transfer period (M) is the minimum time allowed between leading edges of successive REQ pulses and of succes-
sive ACK pulses to meet the device requirements for successful reception of data. The drive supports trans-
fer period in the range of 50 ns to 425 ns in increments of 25 ns. In addition to this, when the drive is
working in LVD mode, it supports transfer period of 25 ns.
REQ/ACK Offset
X The ACK/REQ offset (X above) is the maximum number of REQ pulses allowed to be outstanding before the leading
edge of its corresponding ACK pulses is received at the drive. A REQ/ACK offset value of zero indicates asynchro-
nous data transfer mode. The drive supports REQ/ACK offset values in the range 0 through 63.
If ATN is negated before all bytes of a multiple-byte extended message is received, the drive will go to BUS FREE to signal a
catastrophic error.
19.1.2.1 Synchronous Negotiation started by the Initiator
When the Target responds with REQ/ACK offset value of 0, the Initiator shall use asynchronous data transfer mode.
Hitachi Ultrastar 15K147 SCSI Hard Disk Drive Specification
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