Seagate Medalist 2160N (ST52160N), Product Manual

Page: 98 / 138

A.2 Synchronous Data Transfer Request message
(01
H
)
The synchronous Data Transfer Request message is an extended mes-
sage.
Depending on the value contained in the SSM bit (contained in byte 2 of
the Operating page in Appendix D.2.2. on page 121), the drive or the
initiator can negotiate for synchronous data transfer after a reset. If any
problem precludes the successful exchange of synchronous Data Trans-
fer Request messages, the initiator and drive default to asynchronous
data transfers. Also, reception of a Wide Data Transfer Request message
sets the drive to the default asynchronous transfers.
This exchange of messages establishes the minimum transfer period and
the maximum allowed REQ/ACK offset.
Bytes
Bits
7 6 5 4 3 2 1 0
0 Extended message (01
H
)
1 Extended message length (03
H
)
2 Identifier code (01
H
)
3 Minimum transfer period divided by 4
4 REQ/ACK offset
Byte 0 This byte identifies the message as an extended message.
Byte 1 This byte reports the length of the message.
Byte 2 This byte identifies the message as a synchronous data transfer
request message.
Byte 3 The value contained in this byte is in nsec. It is equal to the
minimum period in which the device can receive data, in units of
4 nsec. In byte 3, the minimum value supported by the drive is
0C
H
, which is equivalent to a transfer period of 48 nsec, or a
maximum external transfer rate of 20 Mbytes per second. A
value of 19
H
is equivalent to a transfer period of 100 nsec, or a
maximum external transfer rate of 10 Mbytes per second. A
value of 32
H
is equivalent to a transfer period of 200 nsec, or a
maximum external transfer rate of 5 Mbytes per second.
Byte 4 The REQ/ACK offset is the maximum number of REQ pulses
that may be outstanding before its corresponding ACK pulse is
received at the target. A REQ/ACK offset of zero indicates
asynchronous mode. The drive supports a maximum REQ/ACK
offset of 0F
H
.
88 Medalist Pro 2160N/2160WC Product Manual, Rev. A