4.6Messages

This section describes the detection of an ATN signal and explains the types of messages supported by this scanner.

4.6.1ATN detection

The following table summarizes the timing at which this scanner detects an ATN signal.

Phase

ATN detection timing

 

 

SELECTION

Immediately before a phase change

 

 

COMMAND

Immediately before a phase change

 

 

DATA OUT

Immediately before a phase change

 

 

DATA IN

Immediately before a phase change (*1)

 

 

STATUS

Immediately before a phase change

 

 

MESSAGE OUT

Upon each reception of a message

 

 

MESSAGE IN

Upon each transmission of a message

 

 

*1 This scanner detects ATU signal for every Read command during an image data transmission. When an ATN signal is detected, scanning operation is interrupted.

4.6.2Message types

Messages provide information consisting of one or more bytes that are transferred in the MESSAGE IN and MESSAGE OUT phases. These messages are used to control the bus phase sequence.

The initiator creates an ATTENTION condition for the target, indicating that it has a message to be reported to the target. Only then the target switches to the MESSAGE OUT phase to receive the message.

If the target has completed the SELECTION/RESELECTION phase, it can execute the MESSAGE IN phase at any time to send the message to the initiator.

The messages that can be communicated with this scanner are listed in the following table.

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