Canon PIXMA MG4200 Series On-Screen Manual page 854

The card slot is used as the memory card drive of a computer connected to the machine via a network.
Data can be written on the memory card from the computer.
Not writable from PC
The card slot is used only for reading. Be sure to select this mode when printing photos from a
memory card.
Important
When Writable from USB PC or Writable from LAN PC is selected, the auto power off setting is
inactive.
For details on the auto power off setting:
About ECO settings
Important
If you use the card slot as the memory card drive of the computer, you need to perform a "safe
removal" operation on your computer before physically removing the memory card from your machine.
Drag the (Mount drive) icon into the Trash.
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