LANCAM A/L series (not recommended for new designs)
General Description
GENERAL DESCRIPTION
The LANCAM A/L series consists of various depths of
64-bit Content Addressable Memories (CAMs), with a
16-bit wide interface.
CAMs, also known as associative memories, operate in the
converse way to random access memories (RAM). In
RAM, the input to the device is an address and the output
is the data stored at that address. In CAM, the input is a
data sample and the output is a flag to indicate a match and
the address of the matching data. As a result, CAM
searches large databases for matching data in a short,
constant time period, no matter how many entries are in
the database. The ability to search data words up to 64 bits
wide allows large address spaces to be searched rapidly
and efficiently. A patented architecture links each CAM
entry to associated data and makes this data available for
use after a successful compare operation.
The MUSIC LANCAMs are ideal for address filtering and
translation applications in LAN switches and routers. The
LANCAMs are also well suited to encryption, database
accelerators, and image processing.
OPERATIONAL OVERVIEW
To use the LANCAM, the user loads the data into the
Comparand register, which is automatically compared to
all valid CAM locations. The device then indicates
whether or not one or more of the valid CAM locations
contains data that matches the target data. The status of
each CAM location is determined by two validity bits at
each memory location. The two bits are encoded to render
four validity conditions: Valid, Empty, Skip, and RAM,
shown in Status Register Bits on page 24 (bits 29:28). The
memory can be partitioned into CAM and associated
RAM segments on 16-bit boundaries, but by using one of
the two available Mask registers, the CAM/RAM
partitioning can be set at any arbitrary size between zero
and 64 bits.
The LANCAM’s internal data path is 64 bits wide for
rapid internal comparison and data movement. Vertical
cascading of additional LANCAMs in a daisy chain
fashion extends the CAM memory depth for large
databases. Cascading requires no external logic. Loading
data to the Control, Comparand, and Mask registers
automatically triggers a compare. Compares also may be
initiated by a command to the device. Associated RAM
data is available immediately after a successful compare
operation. The Status register reports the results of
compares including all flags and addresses. Two Mask
registers are available and can be used in two different
ways: to mask comparisons or to mask data writes. The
RAM validity type allows additional masks to be stored in
the CAM array where they may be retrieved rapidly.
A simple four-wire control interface and commands
loaded into the Instruction decoder control the device. A
powerful instruction set increases the control flexibility
and minimizes software overhead. Additionally, dedicated
pins for match and multiple-match flags enhance
performance when the device is controlled by a state
machine. These and other features make the LANCAM a
powerful associative memory that drastically reduces
search delays.
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Rev. 1
MUSIC [ MUSIC SEMICONDUCTORS ]
