EP2A15 Datasheet, PDF (36/99 Pages) Altera Corporation – Programmable Logic Device Family

APEX II Programmable Logic Device Family Data Sheet
If the same data is written into multiple locations in the memory, a CAM
block can be used in multiple-match or fast multiple-match modes. The
ESB outputs the matched data’s locations as an encoded or unencoded
address. In multiple-match mode, it takes two clock cycles to write into a
CAM block. For reading, there are 16 outputs from each ESB at each clock
cycle. Therefore, it takes two clock cycles to represent the 32 words from
a single ESB port. In this mode, encoded and unencoded outputs are
available. To implement the encoded version, the Quartus II software
adds a priority encoder with LEs. Fast multiple-match is identical to the
multiple match mode, however, it only takes one clock cycle to read from
a CAM block and generate valid outputs. To do this, the entire ESB is used
to represent 16 outputs. In fast multiple-match mode, the ESB can
implement a maximum CAM block size of 16 words.
A CAM block can be pre-loaded with data during configuration, or it can
be written during system operation. In most cases, two clock cycles are
required to write each word into CAM. When don’t-care bits are used, a
third clock cycle is required.
f For more information on CAM, see Application Note 119 (Implementing
High-Speed Search Applications with APEX CAM).
Driving Signals to the ESB
ESBs provide flexible options for driving control signals. Different clocks
can be used for the ESB inputs and outputs. Registers can be inserted
independently on the data input, data output, read address, write
address, WE, and RE signals. The global signals and the local interconnect
can drive the WE and RE signals. The global signals, dedicated clock pins,
and local interconnects can drive the ESB clock signals. Because the LEs
drive the local interconnect, the LEs can control the WE and RE signals and
the ESB clock, clock enable, and synchronous clear signals. Figure 24
shows the ESB control signal generation logic.
36
Altera Corporation