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The PARALLEL PROTOCOL REQUEST message negotiates the synchronous
data transfer agreement, the wide data transfer agreement, and set the protocol
options between the host computer and the controller.
If the host computer requests the synchronous data transfer, the wide data
transfer, it shall negotiate with the controller by PARALLEL PROTOCOL
REQUEST message since the default transfer mode of the controller is
asynchronous data transfer and data transfer width 8 bits.
The controller may negotiate with each host computer by PARALLEL PROTOCOL
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 PARALLEL PROTOCOL 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 PARALLEL PROTOCOL REQUEST message from the host
computer, the controller respond with either PARALLEL PROTOCOL REQUEST
or MESSAGE REJECT message.
Table 3.6 shows PARALLEL PROTOCOL 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(06
). The extended message length does not include itself.
H)
The code 04
The Transfer period(mm
allowed between leading edges of successive REQ signals and successive ACK
signals ( period of REQ signal and ACK signal ).
The REQ / ACK offset(XX
outstanding before its corresponding ACK signal is received at the controller.
A REQ / ACK offset value of zero indicates asynchronous mode, a value of FF
indicates unlimit offset.
3 SCSI BUS
in byte 2 indicates PARALLEL PROTOCOL REQUEST message.
H
) specifies the minimum time ( 4 ns as increment )
H
) is the maximum number of REQ signals allowed to be
H
OEM MANUAL:K6602924
Revision: 1 / Date: 2003.03.06
Page: 46 / 273
H
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