One-Byte Messages; Two-Byte Messages; Extended Messages; Message Categories - Seagate Ultra160 Product Manual

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Message code Message format
55h One-byte message
56–7Fh Reserved
80h–FFh One-byte message (IDENTIFY)
4.2.1

One-byte messages

One-byte messages consist of a single byte transferred during a MESSAGE phase. The byte's message code
determines the message to be performed as defined in Tables 26, 39, and 44. The IDENTIFY message is a
one-byte code, but its format is different.
4.2.2

Two-byte messages

Two-byte messages consist of two consecutive bytes transferred during a MESSAGE IN phase or a MESSAGE
OUT phase. The value of the first byte determines the message to be performed as defined in Tables 26, 39,
and 44. The second byte is a parameter byte used as defined in the message descriptions.
4.2.3

Extended messages

A value of 01h in 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. All of the extended message bytes shall be
transferred in consecutive MESSAGE IN phases or consecutive MESSAGE OUT phases. See sections refer-
enced in Table 25 for details of the extended messages.
Table 24: Extended message format
Bit 7
Byte
0 EXTENDED MESSAGE (01h)
1 EXTENDED MESSAGE LENGTH (n–1) [1]
2 EXTENDED MESSAGE CODE [2]
3-n EXTENDED MESSAGE ARGUMENTS [3]
[1] The EXTENDED MESSAGE LENGTH field specifies the length in bytes of the Extended Message Code
plus the extended message arguments to follow. The total length of the message is equal to the
EXTENDED MESSAGE LENGTH plus two. A value of zero in the EXTENDED MESSAGE LENGTH field
indicates 256 bytes follow.
[2] The extended message codes are listed in Table 25.
Table 25: Extended Message Codes
Code Extended message
00h MODIFY DATA POINTERS
01h SYNCHRONOUS DATA TRANSFER REQUEST
02h Reserved
03h WIDE DATA TRANSFER REQUEST
04h PARALLEL PROTOCOL REQUEST
05h MODIFY BIDIRECTIONAL DATA POINTER
06h - FFh Reserved
[3] The EXTENDED MESSAGE ARGUMENTS are specified within the Extended Message Descriptions in
Paragraphs referenced in Table 26.
4.3

Message categories

The messages supported by the various drives are divided up into categories and listed in tables in the follow-
ing subsections. The individual drive's Product Manual, Volume 1. Table 26 lists messages that are supported
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SCSI Interface Product Manual, Rev. B
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