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A-61124 March 1999 2-3
When an error occurs, the host will receive a SCSI Check
Condition Status. This indicates to the host that there may be
one current error and potentially one or more deferred errors.
The host must follow a Check Condition Status with a SCSI
Request Sense command. The Sense data will indicate the type
of error that has occurred.
To receive subsequent pending errors , the host must execute a
SCSI Test Unit Ready command. If a deferred error is pending,
the Test Unit Ready command will terminate with a Check
Condition Status. The host follows with a SCSI Request Sense
command. The combination of Request Sense followed by Test
Unit Ready must be repeated until a "good" status is returned on
the Test Unit Ready command. A "good" status indicates no
errors (current or deferred) are pending.
IMPORTANT:
If at any point the host receives a Check Condition
for a command and fails to issue a subsequent
Request Sense command, the scanner will clear
all (current and deferred) Sense data.
Some error conditions disable scanning and cause the document
transport to stop. These errors are reported on the scanner
control panel. This is done to prevent additional images from
entering the image buffer while allowing the host to perform fault
recovery activities. To aid in fault recovery, the information bytes
of the Request Sense data will contain a Sequential ID Number
for the approximate image upon which the error occurred.
NOTE: The scanner cannot determine exactly which images were
affected by the error and which images were not.
If an error occurs that disables the scanner, the host can continue
to read images from the image buffer without enabling the
scanner. However, when the image buffer has been emptied, an
error will be generated indicating fault recovery is required. This
differentiates between an end-of-job disable and a disable
caused by an error. The operator may continue scanning
documents after the host enables the scanner.