MSM548263 datasheet(35/40 Pages) OKI

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MSM548263

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Read Transfer: RAS falling edge --- CAS = WE = "H", TRG = DSF = "L"

Read transfer consists of loading a selected row of data from the RAM into the SAM register. A

read transfer is invoked by holding CAS "high", TRG "low", WE "high", and DSF "low" at the

falling edge of RAS. The row address selected at the falling edge of RAS determines the RAM row

to be transferred into the SAM. The transfer cycle is completed at the rising edge of TRG. When

the transfer is completed, the SAM port is set into the output mode. In a read/real time read

transfer cycle, the transfer of a new row of data is completed at the rising edge of TRG, and this

data becomes valid on the SDQ lines after the specified access time tSCA from the rising edge of

the subsequent SC cycles. The start address of the serial pointer of the SAM is determined by the

column address selected at the falling edge of CAS. In a read transfer cycle (which is preceded

by a write transfer cycle), SC clock must be held at a constant VIL or VIH after the SC high time

has been satisfied. A rising edge of the SC clock must not occur until after the specified delay tTSD

from the rising edge of TRG.

In a real time read transfer cycle (which is preceded by another read transfer cycle), the previous

row data appears on the SDQ lines until the TRG signal goes "high", and the serial access time

tSCA for the following serial clock is satisfied. This feature allows for the first bit of the new row

of data to appear on the serial output as soon as the last bit of the previous row has been strobed

without any timing loss. To make this continuous data flow possible, the rising edge of TRG must

be synchronized with RAS, CAS, and the subsequent rising edge of SC (tRTH, tCTH, and tTSL/tTSD

must be satisfied).

Masked Write Transfer: RAS falling edge --- CAS = "H", TRG = WE = DSF = "L"

Write transfer cycle consists of loading the content of the SAM register into a selected row of the

RAM. This write transfer is the same as a mask write operation in RAM, so new and persistent

(old) mask mode can be supported. (Masked write transfer)

If the SAM data to be transferred must first be loaded through the SAM, a Masked write transfer

operation (all DQ pins "low" at falling edge of RAS) must precede the write transfer cycles. A

masked write transfer is invoked by holding CAS "high", TRG "low", WE "low" and DSF "low"

at the falling edge of RAS. The row address selected at the falling edge of RAS determines the

RAM row address into which the data will be transferred. The column address selected at the

falling edge of CAS determines the start address of the serial pointer of the SAM. After the write

transfer is completed, the SDQ lines are set in the input mode so that serial data synchronized

with the SC clock can be loaded.

When consecutive write transfer operations are performed, new data must not be written into

the serial register until the RAS cycle of the preceding write transfer is completed. Consequently,

the SC clock must be held at a constant VIL or VIH during the RAS cycle. A rising edge of the SC

clock is only allowed after the specified delay tCSD from the falling edge of the CAS, at which time

a new row of data can be written in the serial register.

Data transferred to SAM by read transfer cycle or split read transfer cycle can be written to the

other address of RAM by write transfer cycle. However, the address to write data must be the

same as that of the read transfer cycle (row address AX8).

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