Filter
Top Products
Host Interface
4-42 C156-E224-01EN
4.4 SCSI Messages
SCSI messages are used to control the SCSI bus operating sequence. This section
explains how SCSI messages work.
4.4.1 Message formats
There are three types of message formats. In any format, the first byte of each
message is a message code (see Table 4.73).
• 1-byte message: Only the message code
• 2-byte message: Message with a message code from 20h to 2Fh. Each 2-
byte message consists of a 1-byte message code and a 1-
byte parameter. (The ODD does not support this type of
messages).
• Extended message: Multiple-byte message with message code 01h. An
extended message code and message length are defined
in each message.
4.4.2 Message types
Table 4.73 lists the types of messages provided by the ODD.
Table 4.73 Types of messages provided by ODD
Message
code (hex)
Message
Byte
count
Transfer direction
ATN
release
00 Command Complete 1
TARG → INIT
01
Extended Message
(Synchronous Data Transfer
Request)
n+2
(5)
TARG ←→ INIT
INIT
02 Save Data Pointer 1
TARG → INIT
04 Disconnect 1
TARG → INIT
05 Initiator Detected Error 1
TARG ← INIT
INIT
06 Abort 1
TARG ← INIT
INIT
07 Message Reject 1
TARG ← INIT
INIT
08 No Operation 1
TARG ← INIT
INIT
09 Message Parity Error 1
TARG ← INIT
INIT
0C Bus Device Reset 1
TARG ← INIT
INIT
80
↓
FF
Identify 1
TARG ←→ INIT