Epson GT-12000 User Manual page 24

Terminator
The scanner has a built-in terminator. If the scanner is the only
SCSI device you connect to your computer or if it is the last
device in the daisy chain, leave the internal SCSI terminator
turned on. It is on if the switch is up.
If the scanner is in the middle of a daisy chain, turn the
terminator switch off.
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Setting Up the Scanner