M7020R datasheet(100/150 Pages) STMICROELECTRONICS

100 / 150 page

M7020R

100/150

The following is the sequence of operation for a

single 272-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 used for

bits [271:136] of the data being searched.

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

([271:204])to be compared to all locations “0” in

the four 68-bit-word page. The CMD[2] signal

must be driven to logic '1.'

Note: CMD[2] = 1 signals that the search is a

x272-bit search. CMD[8:7] is ignored in this cy-

cle.

– Cycle B: The host ASIC continues to drive the

CMDV high and applies SEARCH command

('10') on CMD[1:0]. The DQ[67:0] is driven with

the 68-bit data ([203:136]) to be compared to all

locations '1' in the four 68-bits-word page.

– Cycle C: 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 used for

the bits [135:0] of the data being searched.

CMD[8:7] signals must be driven with the bits

that

will

driven

this

device

SADR[21:20] if it has a hit. DQ[67:0] must be

driven with the 68-bit data ([135:68]) to be com-

pared to all locations “2” in the four 68-bit-word

page. The CMD[2] signal must be driven to logic

'0.'

– Cycle D: The host ASIC continues to drive the

CMDV high and continues to apply SEARCH

command code ('10') on CMD[1:0]. 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 the 68-bit data ([67:0]) to

be compared to all locations “3” in the four 68-

bit-word page. CMD[5:2] is ignored because the

LEARN Instruction is not supported for x272 ta-

bles.

Note: For 272-bit searches, the host ASIC must

supply four distinct 68-bit data words on

DQ[67:0] during Cycles A, B, C, and D. The

GMR Index in Cycle A selects a pair of GMRs in

each of the 31 devices that apply to DQ data in

Cycles A and B. The GMR Index in Cycle C se-

lects a pair of GMRs in each of the 31 devices

that apply to DQ data in Cycles C and D.

The logical 272-bit SEARCH operation is as

shown in Figure 73, page 103. The entire table of

272-bit entries is compared to a 272-bit word K

that is presented on the DQ Bus in Cycles A, B, C,

and D of the command using the GMR and local

mask bits. The GMR is the 272-bit word specified

by the two pairs of GMRs selected by the GMR In-

dexes in the command’s Cycles A and C in each

of the 31 devices. The 272-bit word K that is pre-

sented on the DQ Bus in Cycles A, B, C, and D of

the command is compared to each entry in the ta-

ble starting at location “0.” The first matching en-

try’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 ADDRESSING,

page 126).

Note: The matching address is always going to be

location “0” in a four-entry page for 272-bit search

(two LSBs of the matching index will be '00').

The SEARCH command is a pipelined operation

and executes a search at one-fourth the rate of the

frequency of CLK2X for 272-bit searches in x272-

configured tables. The latency of SADR, CE_L,

ALE_L, WE_L, SSV, and SSF from the 272-bit

SEARCH command (measured in CLK cycles)

from the CLK2X cycle that contains Cycles C and

D shown in Table 47, page 115.

The latency of a SEARCH from command to

SRAM access cycle is 6 for only a single device in

the table and TLSZ = 10. In addition, SSV and SSF

shift further to the right for different values of

HLAT, as specified in Table 48, page 115

The 272-bit SEARCH operation is pipelined and

executes as follows:

– Four cycles from the last cycle of the SEARCH

command each of the devices knows the out-

come internal to it for that operation.

– In the fifth cycle from the SEARCH command,

the devices in a block (which is less than or

equal to eight devices resolving the winner with-

in them using an LHI[6:0] and LHO[1:0] signal-

ling mechanism) arbitrate for a winner.

– In the sixth cycle after the SEARCH command,

the blocks of devices resolve the winning block

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

mechanism. The winning device within the win-

ning block is the global winning device for the

SEARCH operation.

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