M7020R datasheet(73/150 Pages) STMICROELECTRONICS

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M7020R

The following is the sequence of operation for a

single 136-bit SEARCH command (see COM-

MAND CODES AND PARAMETERS, page 29).

– Cycle A: The host ASIC drives the CMDV high

and applies SEARCH command code ('10') on

CMD[1:0] signals. CMD[5:3] signals must be

driven with the index to the GMR pair for use in

this SEARCH operation. CMD[8:7] signals must

be driven with the bits that will be driven on

SADR[21:20] by this device if it has a hit.

DQ[67:0] must be driven with the 68-bit data

([135:68]) in order to be compared against all

even locations. The CMD[2] signal must be driv-

en to logic '0.'

– Cycle B: The host ASIC continues to drive the

CMDV high and to apply SEARCH command

code ('10') on CMD[1:0]. CMD[5:2] must be driv-

en by the index of the comparand register pair

for storing the 136-bit word presented on the DQ

Bus during Cycles A and B. CMD[8:6] signals

must be driven with the index of the SSR that

will be used for storing the address of the

matching entry and the Hit Flag (see SEARCH-

Successful Registers (SSR[0:7]), page 23). The

DQ[67:0] is driven with 68-bit data ([67:0]) to be

compared against all odd locations.

The logical 136-bit SEARCH operation is as

shown in Figure 51, page 76. The entire table of 31

devices (consisting of 136-bit entries) is compared

against a 136-bit word K that is presented on the

DQ Bus in Cycles A and B of the command using

the GMR and local mask bits. The GMR is the 136-

bit word specified by the even and odd global

mask pair selected by the GMR Index in the com-

mand’s Cycle A.

The 136-bit word K that is presented on the DQ

Bus in Cycles A and B of the command is also

stored in the even and odd comparand registers

specified by the Comparand Register Index in the

command’s Cycle B. In x136 configurations, the

even and odd comparand registers can subse-

quently be used by the LEARN command in only

the first non-full device.

Note: The LEARN command is supported for only

one of the blocks consisting of up to eight devices

in a depth-cascaded table of more than one block.

The word K that is presented on the DQ Bus in Cy-

cles A and B of the command is compared with

each entry in the table starting at location “0.” The

first matching entry’s location address, “L,” is the

winning address that is driven as part of the SRAM

address on the SADR[21:0] lines (see SRAM AD-

DRESSING, page 126). The global winning device

will drive the bus in a specific cycle. On global miss

cycles the device with LRAM = 1 (the default driv-

ing device for the SRAM bus) and LDEV = 1 (the

default driving device for SSF and SSV signals)

will be the default driver for such missed cycles.

Note: During 136-bit searches of 136-bit-config-

ured tables, the search hit will always be at an

even address.

The SEARCH command is a pipelined operation.

It executes a search at half the rate of the frequen-

cy of CLK2X for 136-bit searches in x136-config-

ured tables. The latency of SADR, CE_L, ALE_L,

WE_L, SSV, and SSF from the 136-bit SEARCH

command cycle (two CLK2X cycles) is shown in

Table 39, page 88.

The latency of a search from command to the

SRAM access cycle is 6 for 1–31 devices in the ta-

ble and where TLSZ = 10. In addition, SSV and

SSF shift further to the right for different values of

HLAT, as specified in Table 40, page 88.

The 136-bit SEARCH operation is pipelined and

executes as follows:

– Four cycles from the SEARCH command, each

of the devices knows the outcome internal to it

for that operation.

– In the fifth cycle after the SEARCH command,

the devices in a block (being less than or equal

to eight devices resolving the winner within

them using the LHI[6:0] and LHO[1:0] signalling

mechanism) arbitrate for a winner amongst

them.

– In the sixth cycle after the SEARCH command,

the blocks (of devices) resolve the winning block

through the BHI[2:0] and BHO[2:0] signalling

mechanism. The winning device in the winning

block is the global winning device for a

SEARCH operation.

Table 38. Hit/Miss Assumption

Search Number

1234

Block 0

Miss

Block 1

Miss

Hit

Miss

Block 2

Miss

Hit

Miss

Block 3

Hit

Miss

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