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EXTENDED MESSAGE (01h)
5.3.2.
5.3.2.1.
SYNCHRONOUS DATA TRANSFER REQUEST(01h)
This is sent by either the initiator or the target as the first byte of a multiple-byte message. When acting as an initiator,
the unit will not send any Extended Messages. No Vendor Unique codes are implemented and only the Synchronous
Data Transfer Request code is supported. Any other message code is handled as an illegal message; the unit will
return MESSAGE REJECT and will continue. A Synchronous Data Transfer Request message has the following
format:
Byte
Value
0
01h
1
03h
2
01h
3
M
4
X
A SYNCHRONOUS DATA TRANSFER REQUEST (SDTR) message exchange shall be initiated by a 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 hard reset condition
(2) after a BUS DEVICE RESET message and
(3) after a power cycle.
In addition, a SCSI device may initiate an SDTR message exchange whenever it is appropriate to negotiate a new
data transfer agreement (either synchronous or asynchronous). SCSI devices that are capable of synchronous data
transfers shall not respond to an SDTR message with a MESSAGE REJECT message.
The SDTR message exchange establishes the permissible transfer periods and the REQ/ACK offsets for all logical
units and target routines on the two devices. This agreement only applies to data phases. The transfer period factor
times four is the value of the transfer period.
Transfer period is the minimum time allowed between leading edges of successive REQ pulses and of successive
ACK pulses. The SDX-250V supports the following transfer periods:
Transfer Period (hex)
Transfer Rate (MB/s) - narrow
Transfer Rate (MB/s)- wide
REQ/ACK offset: is the maximum number of REQ pulses allowed to be outstanding before the leading edge of its
corresponding ACK pulse is received at the target. A REQ/ACK offset value of ZERO shall indicate asynchronous
data transfer mode. The SDX-250V supports synchronous data transfer REQ/ACK offset values from 1 to 15.
The originating device (the device that sends the first of the pair of SDTR messages) sets its values according to the
rules above to permit it to receive data successfully. If the responding device can also receive data successfully with
these values (or smaller transfer periods or larger REQ/ACK offsets or both), it returns the same values in its SDTR
message. If it requires a larger transfer period, a smaller REQ/ACK offset, or both in order to receive data
successfully, it substitutes values in its SDTR message as required, returning unchanged any value not required to
be changed. Each device when transmitting data shall respect the limits set by the other's SDTR message, but it is
permitted to transfer data with larger transfer periods, smaller REQ/ACK offsets, or both than specified in the other's
SDTR message. The successful completion of an exchange of SDTR messages implies an agreement as follows:
SONY AIT-E Turbo drive SDX-250V series Ver.1.0
Table 5-3: Synchronous Data Transfer Request
Extended message
Extended message length
SYNCHRONOUS DATA TRANSFER REQUEST code
Transfer period (m times 4 nanoseconds)
REQ/ACK offset
Table 5-4: Synchronous Data Transfer Rates
0C
19
20.0
10.0
40.0
20.0
Description
1F
26
2C
8.0
6.67
5.71
16.0
13.34
11.42
5.SCSI Interface
32
38
5.00
4.44
10.00
8.88
5-5
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