Chapter 2 Scsi Message; Message System; Message Format - Fujitsu MBA3073 SERIES Technical Manual

CHAPTER 2
This chapter describes SCSI messages and their operations for controlling the operation sequence of the
SCSI bus.
Note:
The HDD operates as a target device (TARG) on the SCSI bus. The HDD is referred to as the
TARG in this chapter except when its clear identification is required.
2.1

Message System

The message system provides procedures for information (or message) transfer between two SCSI
devices on the SCSI bus in order to control a series of bus phase sequence during command
execution. The messages are transferred over the SCSI data bus in the MESSAGE OUT and
MESSAGE IN phases.
2.1.1

Message format

There are three message formats are listed below. The first byte of the message is a message code
in any format. (See Figure 2.1.)
•
One-byte message: This consists of a message code only.
•
Two-byte message: Message code is between X'20' and X'2F'. This consists of a message
•
Extended message: This is a message of multiple bytes length message code of X'01'.
C141-C015
SCSI MESSAGE
2.1 Message System
2.2 SCSI Pointer
2.3 Message Explanation
code and one-byte length parameter.
The Extended message code and message length are specified in the
message.
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