Content addressable memory (CAM) devices include CAM logic that is
configured to pass an instruction received at an instruction input port
to an instruction output port without inspection or alteration. This
enables the CAM devices to be operated as equivalent devices within a
cascaded chain of CAM devices that collectively form multiple databases
within a lookup engine having distributed CAM control. This CAM logic may
include an input instruction register that is configured to latch the
instruction received at the instruction input port and an output
instruction register that is configured to latch the instruction received
from the input instruction register. This CAM logic may also include an
instruction FIFO that is configured to buffer instructions received from
the input instruction register. A method of performing a learn operation
in a cascaded chain of CAM devices may include writing a search key
associated with a database into a selected one of the cascaded chain of
CAM devices, in response to evaluating whether an NFA table in the
selected one of the cascaded chain of CAM devices has a valid NFA address
for the search key. Then, following the write operation, an operation may
be performed to search each of the CAM devices in the cascaded chain to
identify an address of a highest priority invalid entry in a CAM device
that retains at least a portion of the database.