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Altera Corporation
APEX 20K Programmable Logic Device Family Data Sheet
Single-Port Mode
The APEX 20K ESB also supports a single-port mode, which is used when
simultaneous reads and writes are not required. See
Figure 22.Figure 22. ESB in Single-Port Mode
Notes:
(1)
All registers can be asynchronously cleared by ESB local interconnect signals, global signals, or the chip-wide reset.
(2)
APEX 20KE devices have four dedicated clocks.
Content-Addressable Memory
In APEX 20KE devices, the ESB can implement CAM. CAM can be
thought of as the inverse of RAM. When read, RAM outputs the data for
word. For example, if the data FA12 is stored in address 14, the CAM
outputs 14 when FA12 is driven into it.
CAM is used for high-speed search operations. When searching for data
within a RAM block, the search is performed serially. Thus, finding a
particular data word can take many cycles. CAM searches all addresses in
parallel and outputs the address storing a particular word. When a match
is found, a match flag is set high.
Figure 23 shows the CAM block
diagram.
Dedicated Clocks
2 or 4
4
D
ENA
Q
D
ENA
Q
D
ENA
Q
D
ENA
Q
data[ ]
address[ ]
RAM/ROM
128
× 16
256
× 8
512
× 4
1,024
× 2
2,048
× 1
Data In
Address
Write Enable
Data Out
outclken
inclken
inclock
outclock
Write
Pulse
Generator
wren
Dedicated Inputs &
Global Signals
to MegaLAB,
FastTrack &
Local
Interconnect
(2)