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Chapter 7 SCSI Interface
The autoloader performs the following processing depending on the setting of
protocol option bits QAS_REQ, DT_REQ, and U_REQ.
Table 7.2.1.9 : Valid protocol options bit combinations
QAS_REQ, DT_REQ, and IU_REQ: Because DT synchronous data transfer is
not supported, only zero is valid for these values.
If the autoloader receives this message, it performs the following processing.
Table 7.2.1.10 : PARALLEL PROTOCOL REQUEST messages implied agreements
02h: SAVE DATA POINTER
The SAVE DATA POINTER message is an indication from the autoloader to
the host to save the data pointer relating to the autoloader currently active. The
autoloader returns this before disconnecting.
03h: RESTORE POINTER
The RESTORE POINTER message is an indication from the autoloader to the
host to restore the most recently saved data pointer relating to the autoloader.
04h: DISCONNECT
The DISCONNECT message is an indication from the autoloader to the host to
disconnect from the SCSI bus. After issuing this message, a RESELECTION is
performed to complete the current processing. If the autoloader receives this
message, it is treated as an illegal message and MESSAGE REJECT is returned.
QAS_REQ DT_REQ IU_REQ
Description
0
0
0
Use ST DATA IN and ST DATA OUT phases to
transfer data
0
1
0
Use DT DATA IN and DT DATA OUT phases with
data group transfers (not supported)
0
1
1
Use DT DATA IN and DT DATA OUT phase with
information unit transfers (not supported)
1
1
1
Use DT DATA IN and DT DATA OUT phases with
information unit transfers and use QAS for
arbitration (not supported)
Loader's PARALLEL PROTOCOL REQUEST
response
Implied agreement
Non-zero REQ/ACK offset
Synchronous transfer
REQ/ACK offset = 0
Asynchronous transfer
TRANSFER WIDTH EXPONENT = 1
16-bit data transfer
TRANSFER WIDTH EXPONENT = 0
8-bit data transfer
Transfer period factor = 9h
( and protocol option = 0h )
8-bit data transfer/
asynchronous data transfer
MESSAGE REJECT message
8-bit data transfer/
asynchronous data transfer
Parity error (on responding message)
8-bit data transfer/
asynchronous data transfer
Unexpected bus free (as a result of the responding
message)
8-bit data transfer/
asynchronous data transfer
No response
8-bit data transfer/
asynchronous data transfer
