Epson GT-6500 EN - Manual (Page 92)

Problem:
The scanner scans properly when you use a bi-directional
parallel interface, but when you switch to SCSI, the scanner no
longer operates properly.
Cause
During block data transfer mode, your program does
not read the entire block at one time, but performs
multiple read commands for each data block.
Solution
Change your program so it reads the entire block in
one read operation.
Problem:
After using a scanner option (Automatic Document Feeder or
Transparency Unit), a different program attempts scanning.
Although the second program tries to scan without using the
option, the option remains operational.
Cause
Your program did not exit option mode upon
completion.
Solution
Always exit option mode upon program completion.
2-54 Command Usage