Tandberg Data
Message System
6-5
Tandberg SLR Product Line SCSI Functional Specifications
6.3.
Extended Message
A value of one (01h) of the first byte of a message
indicates the beginning of a multiple-byte extended
message. The minimum number of bytes sent for an
extended message is three. The extended message format
is shown in the table below.
Byte
Value
Description
0
01h
Extended Message
1
n
Extended Message Length
2
y
Extended Message Code
3 - n+1
x
Extended Message Arguments
Table 6-4: Extended Message Format
The extended message length specifies the length in
bytes of the extended message code plus the extended
message arguments to follow. Therefore, the total length
of the message is equal to the extended message length
plus two. A value of zero for the extended message
length indicates 256 bytes to follow.
The extended messages supported by the are shown in the
table below. The extended messages are described in
detail in Sections 6.3.1 and 6.3.2.
Extended Message Code
Description
01h
Synchronous Data Transfer Request
03h
Wide Data Transfer Request
Table 6-5: Supported Extended Message Codes
To comply with the ANSI standard [2] and [5], Wide Data
Transfer must be negotiated prior to negotiating
Synchronous Data Transfer. If a Synchronous Data
Transfer agreement is in effect, it will be reset to
asynchronous mode if the Wide Data Transfer Request is
accepted.
If a parity error is detected during a MESSAGE-OUT phase
the Drive will consume all the remaining bytes in the
message and ask for a re-transfer of the whole message.
If a parity error is detected during a MESSAGE-IN phase
the Initiator may signal a parity error by transferring
a MESSAGE PARITY message back to the Drive. The Drive
responds by transferring the whole message once more.
