M7020R datasheet(136/150 Pages) STMICROELECTRONICS

136 / 150 page

M7020R

136/150

SRAM WRITE with a Table of One Device

SRAM WRITE enables WRITE access to the off-

chip SRAM that contains associative data. The la-

tency from the second cycle of the WRITE Instruc-

tion to the address appearing on the SRAM Bus is

the same as the latency of the SEARCH Instruc-

tion, and will depend on the TLSZ value parameter

programmed in the device configuration register.

The following explains the SRAM WRITE opera-

tion accomplished with a table of only one device

of the following parameters: TLSZ = 00, HLAT =

000, LRAM = 1, and LDEV = 1. Figure 100, page

137 shows the timing diagram.

For the following description the selected device

refers to the only device in the table as it is the only

device that will be accessed.

– Cycle 1A: The host ASIC applies the WRITE In-

struction on CMD[1:0] using CMDV = 1. The DQ

Bus supplies the address with DQ[20:19] set to

'10' to select the SRAM address. The host ASIC

selects the device for which the ID[4:0] matches

the DQ[25:21] lines. The host ASIC also sup-

plies SADR[21:20] on CMD[8:7] in this cycle.

Note: CMD[2] must be set to '0' for SRAM

WRITE because Burst WRITEs into the SRAM

are not supported.

– Cycle 1B: The host ASIC continues to apply the

WRITE

Instruction

CMD[1:0],

using

CMDV = 1. The DQ Bus supplies the address

with DQ[20:19] set to '10' to select the SRAM

address.

Note: CMD[2] must be set to '0' for SRAM

WRITE because Burst WRITEs into the SRAM

are not supported.

– Cycle 2: The host ASIC continues to drive

DQ[67:0]. The data in this cycle is not used by

the M7020R device.

– Cycle 3: The host ASIC continues to drive

DQ[67:0]. The data in this cycle is not used by

the M7020R device.

At the end of Cycle 3, a new command can begin.

The WRITE is a pipelined operation. The WRITE

Cycle appears at the SRAM Bus, however, with

the same latency as that of a SEARCH Instruction,

as measured from the second cycle of the WRITE

command.

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