MU9C2480A/L
GENERAL DESCRIPTION
The MU9C2480A and MU9C2480L LANCAMs are 2048 x
64-bit content-addressable memories (CAMs), with a 16-bit
wide interface. They are pin compatible with all devices in the
MUSICLANCAMfamily.
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.
Content-addressable memories, 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
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, Skip, Empty, and Random Access, shown
in Table 1. 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.
Comparand, and mask registers automatically triggers a
compare. Compares may also 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 random access
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.
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,
/W
/CM
LOW
HIGH
LOW
HIGH
Cycle Type
Skip Bit
Empty Bit
Entry Type
Valid
LOW
LOW
HIGH
HIGH
Command Write Cycle
Data Write Cycle
Command Read Cycle
Data Read Cycle
0
0
1
1
0
1
0
1
Empty
Skip
RAM
Table 2: I/O Cycles
Table 1: Entry Types vs. Validity Bits
Rev. 1a
2
MUSIC [ MUSIC SEMICONDUCTORS ]
