Epson GT-6500 EN - Manual (Page 82)

Error Processing
EPSON scanners have four types of potential errors: command errors,
communications errors, system errors, and option errors. An option
error can occur only with scanner models
on which the optional Automatic Document Feeder or Transparency
Unit can be installed.
When an error occurs, the LED indicator displays the error type. For
details, see the scanner’s user’s manual.
Command error
This error occurs when the scanner receives an incorrect command or
a command with incorrect parameters.
Cause:
The scanner receives an undefined command.
The scanner receives a command with incorrect parameters.
Scanner’s response:
The scanner returns a NAK code to the computer, ignores the
incorrect command or parameters, and waits for the next command.
Error recovery procedure:
Send a correct command; the scanner then clears the error condition.
Communications error
A communication error occurs when the scanner and computer cannot
communicate properly.
Cause:
The interface is disconnected or not connected properly.
2-44 Command Usage