M7020R datasheet(18/150 Pages) STMICROELECTRONICS

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M7020R

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OPERATION

The following subsections contain command

(CMD and DQ Bus (command and databus), data-

base entry, arbitration logic, pipeline, and SRAM

control, and full logic descriptions.

CMD Bus and DQ Bus

CMD[8:0] carries the CMD and its associated pa-

rameter. DQ[67:0] is used for data transfer to and

from the database entries, which comprise a data

and a mask field that are organized as data and

mask arrays. The DQ Bus carries the SEARCH

data (of the data and mask arrays and internal reg-

isters) during the SEARCH command as well as

the address and data during READ and/or WRITE

operations. The DQ Bus can also carry the ad-

dress information for the flow-through accesses to

the external SRAMs and/or SSRAMs.

Database Entry (Data Array and Mask Array)

Each database entry comprises a data and a mask

field. The resultant value of the entry is ’1,' ’0,’ or

’X (don’t care),’ depending on the value in the data

and mask bits. The on-chip priority encoder se-

lects the first matching entry in the database that

is nearest to location '0.'

Arbitration Logic

When multiple Search Engines are cascaded to

create large databases, the data being searched is

presented to all search engines simultaneously in

the cascaded system. If multiple matches occur

within the cascaded devices, arbitration logic on

the search engines will enable the winning device

(with a matching entry that is closest to address “0”

of the cascaded database) to drive the SRAM bus.

Pipeline and SRAM Control

Pipeline latency is added to give enough time to a

cascaded system’s arbitration logic to determine

the device that will drive the index of the matching

entry on the SRAM bus. Pipeline logic adds laten-

cy to both the SRAM access cycles and the SSF

and SSV signals to align them to the host ASIC re-

ceiving the associated data.

Full Logic

Bit[0] in each of the 68-bit entries has a special

purpose for the LEARN command (0 = empty, 1 =

full). When all the data entries have bit[0] = 1, the

database asserts the FULL Flag, indicating all the

search engines in the depth-cascaded array are

full.

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