W97AH6KB datasheet(43/127 Pages) WINBOND

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W97AH6KB / W97AH2KB

Publication Release Date: May 15, 2014

Revision: A01-001

- 43 -

7.4.12 Auto Precharge Operation

Before a new row in an active bank can be opened, the active bank must be precharged using either the Precharge

command or the auto-precharge function. When a Read or a Write command is given to the LPDDR2 SDRAM, the

AP bit (CA0f) may be set to allow the active bank to automatically begin precharge at the earliest possible moment

during the burst read or write cycle.

If AP is LOW when the Read or Write command is issued, then normal Read or Write burst operation is executed

and the bank remains active at the completion of the burst.

If AP is HIGH when the Read or Write command is issued, then the auto-precharge function is engaged. This feature

allows the precharge operation to be partially or completely hidden during burst read cycles (dependent upon Read

or Write latency) thus improving system performance for random data access.

7.4.13 Burst Read with Auto-Precharge

If AP (CA0f) is HIGH when a Read Command is issued, the Read with Auto-Precharge function is engaged.

LPDDR2-S4 devices start an Auto-Precharge operation on the rising edge of the clock BL/2 or BL/2 - 2 +

RU(tRTP/tCK) clock cycles later than the Read with AP command, whichever is greater. Refer to section 7.4.14.2

“Precharge & Auto Precharge Clarification” table for equations related to Auto-Precharge for LPDDR2-S4.

A new bank Activate command may be issued to the same bank if both of the following two conditions are satisfied

simultaneously.

■ The RAS precharge time (tRP) has been satisfied from the clock at which the auto precharge begins.

■ The RAS cycle time (tRC) from the previous bank activation has been satisfied.

7.4.13.1 Burst Read with Auto-Precharge: RL = 3, BL = 4, RU(tRTP(min)/tCK) = 2

CA0-9

[Cmd]

Nop

Activate

Nop

Read

DQS

RL = 3

Bank M

Col Addr A Col Addr A

DOUT A0

DOUT A1

DOUT A2

DOUT A3

Bank M

Row Addr Row Addr

BL / 2

tRTP

>=tRPpb

CK_t / CK_c

DQS_c

DQS_t

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