Dell P1500 Personal Mono Laser Printer - Manual (Page 55)

The printer is busy receiving and processing data or printing.
The printer is defragmenting the flash memory to reclaim storage
space occupied by deleted resources.
The printer is formatting the flash memory.
The printer is storing resources, such as fonts or macros, in flash
memory.
The printer is printing a directory, font list, menu settings pages, or
Print Quality Test Pages.
What you can do:
Busy:
Wait for the message to clear.
Press and release Cancel to cancel the print job.
Press and hold Cancel to reset the printer.
Defragmenting flash, formatting flash, or programming flash:
Wait for the message to clear.
NOTICE: Do not turn the printer off while this message is displayed.
Printing a directory, a font list, menu settings pages, or Print Quality
Test Pages:
Wait for the pages to print. The Busy message is displayed as
the pages print. The Ready/Data light is on when printing stops.
Press and release Cancel to cancel printing.
Press and hold Cancel to reset the printer.
Receiving/processing data from a host interface:
Wait for the message to clear.
Press and release Cancel to stop processing.
Press and hold Cancel to reset the printer.
What this light sequence means: