MU9C2480A(1998) Ver la hoja de datos (PDF) - Music Semiconductors
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MU9C2480A Datasheet PDF : 28 Pages
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MU9C2480A/L
PIN DESCRIPTIONS Continued
/FF (Full Flag, Output, TTL)
If enabled in the Control register, the /FF output goes LOW
when no empty memory locations exist within the device (and
in the daisy chain above the device as indicated by the /FI
pin). The System Full flag is the /FF pin of the last device in the
daisy chain, and the Next Free address resides in the device
with /FI LOW and /FF HIGH. If disabled in the Control register,
the /FF output only depends on the /FI input (/FF = /FI).
/FI (Full Input, Input, TTL)
The /FI input generates a CAM-Memory-System-Full
indication in vertically cascaded systems. It is connected
to the /FF output of the previous device in the daisy chain.
The /FI pin on the first device in a chain must be tied LOW.
/RESET (Reset, Input, TTL)
/RESET must be driven LOW to place the device in a known
state before operation, which will reset the device to the
conditions shown in Table 4 on page 10. LANCAM ‘A’
devices have a hardware reset that operates in parallel with
the internal Power-on-reset circuitry, and sets the device to
the same condition. For compatibility with the MU9C1480,
the /RESET pin has an internal pull-up resistor and may be
left unconnected. The /RESET pin should be driven by
TTL levels, not directly by an RC timeout. /E must be kept
HIGH during /RESET.
TEST1, TEST2 (Test, Input, TTL)
These pins enable MUSIC production test modes that are
not usable in an application. They should be connected to
ground, either directly or through a pull-down resistor, or
they may be left unconnected. These pins may not be
implemented on all versions of these products.
VCC, GND (Positive Power Supply, Ground)
These pins are the power supply connections to the LANCAM.
VCC must meet the voltage supply requirements in the
Operating Conditions section relative to the GND pins, which
are at zero volts (system reference potential), for correct
operation of the device. All the ground and power pins must
be connected to their respective planes with adequate bulk
and high frequency bypassing capacitors in close proximity
to the device. The MU9C2480A and MU9C2480L are
compatible with the original MU9C1480 connections, and may
be operated at -90 or slower switching characteristics without
the GND connections on pins 1 and 23.
FUNCTIONAL DESCRIPTION
The LANCAM is a content-addressable memory (CAM)
with 16-bit I/O for network address filtering and translation,
virtual memory, data compression, caching, and table lookup
applications. The memory consists of static CAM,
organized in 64-bit data fields. Each data field can be
partitioned into a CAM and a RAM subfield on 16-bit
boundaries. The contents of the memory can be randomly
accessed or associatively accessed by the use of a compare.
During automatic comparison cycles, data in the
Comparand register is automatically compared with the
“Valid” entries in the memory array. The Device ID can be
read using a TCO PS instruction (see Table 12 on page 22).
The data inputs and outputs of the LANCAM are
multiplexed for data and instructions over a 16-bit
I/O bus. Internally, data is handled on a 64-bit basis, since
the Comparand register, the mask registers, and each
memory entry are 64 bits wide. Memory entries are globally
configurable into CAM and RAM segments on 16-bit
boundaries, as described in US Patent 5,383,146 assigned
to MUSIC Semiconductors. Seven different CAM/RAM
splits are possible, with the CAM width going from one to
four segments, and the remaining RAM width going from
three to zero segments. Finer resolution on compare width
is possible by invoking a mask register during a compare,
which does global masking on a bit basis. The CAM subfield
contains the associative data, which enters into compares,
while the RAM subfield contains the associated data, which
is not compared. In LAN bridges, the RAM subfield could
hold, for example, port-address and aging information
related to the destination or source address information
held in the CAM subfield of a given location. In a translation
application, the CAM field could hold the dictionary entries,
while the RAM field holds the translations, with almost
instantaneous response.
Each entry has two validity bits (known as Skip bit and
Empty bit) associated with it to define its particular type:
empty, valid, skip, or RAM. When data is written to the
active Comparand register, and the active Segment Control
register reaches its terminal count, the contents of the
Comparand register are automatically compared with the
CAM portion of all the valid entries in the memory array.
For added versatility, the Comparand register can be barrel-
shifted right or left one bit at a time. A Compare instruction
can then be used to force another compare between the
Comparand register and the CAM portion of memory entries
of any one of the four validity types. After a Read or Move
from Memory operation, the validity bits of the location
read or moved will be copied into the Status register, where
they can be read using Command Read cycles.
Rev. 1a
4
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