OEM MANUAL:K6602924
3 SCSI BUS
Revision: 1 / Date: 2003.03.06
Page: 42 / 273
Synchronous Data Transfer Request (010301mmXX
H
)
Table 3.2 SYNCHRONOUS DATA TRANSFER REQUEST
Byte
Value
Description
0
01
H
Extended message
1
03
H
Extended message length
2
01
H
SYNCHRONOUS DATA TRANSFER REQUEST code
3
mm
H
Transfer period (mm
H
times 4 nanoseconds)
4
XX
H
REQ / ACK offset
The SYNCHRONOUS DATA TRANSFER REQUEST message negotiates the
synchronous data transfer-rate between the host computer and the controller.
If the host computer requests the synchronous data transfer, it shall negotiate
with the controller by SYNCHRONOUS DATA TRANSFER REQUEST message
since the default transfer mode of the controller is asynchronous data transfer.
The controller may negotiate with each host computer by SYNCHRONOUS DATA
TRANSFER REQUEST message released by host computers, it does not request
the negotiation by sending this message from the controller.
This negotiation is valid until RESET condition is occurred ( receipt of BUS
DEVICE RESET message, '' hard " RESET or POWER ON RESET) or the
renegotiation is executed.
Note : In order to keep better performance, it is suggested for user not to
negotiate at each SELECTION.
The SYNCHRONOUS DATA TRANSFER REQUEST message is received after
receipt of IDENTIFY message of SELECTION phase ( includes SCSI ID for both
the host computer and the controller ).
In accordance with SYNCHRONOUS DATA TRANSFER REQUEST message from
the host computer, the controller respond with either SYNCHRONOUS DATA
TRANSFER REQUEST or MESSAGE REJECT message.
Table 3.2 shows SYNCHRONOUS DATA TRANSFER REQUEST message which
is used for both the request from the host computer and the response from the
controller.
The extended message length specifies the length in bytes of the following bytes
(03
H
). The extended message length does not include itself.