EtronTech

EM68932DVKB

Etron Confidential

7

Rev. 1.0

Aug. 2009

Mode Register Set(MRS)

The Mode Register stores the data for controlling various operating modes of a DDR SDRAM. It programs

CAS Latency, Burst Type, and Burst Length to make the Mobile DDR SDRAM useful for a variety of

applications. The default value of the Mode Register is not defined; therefore the Mode Register must be

written by the user. Values stored in the register will be retained until the register is reprogrammed, the

device enters Deep Power Down mode, or power is removed from the device. The Mode Register is written

by asserting Low on CS , RAS , CAS , WE , BA1 and BA0 (the device should have all banks idle with no

bursts in progress prior to writing into the mode register, and CKE should be High). The state of address

operation in the Mode Register. The Mode Register is divided into various fields depending on functionality.

The Burst Length uses A0~A2, Burst Type uses A3, and CAS Latency (read latency from column address)

uses A4~A6. A logic 0 should be programmed to all the undefined addresses to ensure future compatibility.

Reserved states should not be used to avoid unknown device operation or incompatibility with future

versions. Refer to the table for specific codes for various burst lengths, burst types and CAS latencies.

Table 4. Mode Register Bitmap

BA1 BA0 A11 A10

A9

A8

A7

A6

A5

A4

A3

A2

A1

A0 Address Field

NOP

PRE

ALL

NOP

*2

Don’t Care

*1: MRS can be issued only with all banks in the idle state.

*2: A minimum delay of tRP is required before issuing an MRS command.

NOP

MRS

*1

NOP

Any

Command

NOP

NOP

CK

CK

Command

Figure 3. de Register Set Cycle

0

0

0

0

0

CAS Latency

BT

Burst Length

Mode Register

A6 A5 A4 CAS Latency

A3 Burst Type

A2 A1 A0

Burst Length

0

0

0

Reserved

0

Sequential

000

Reserved

0

0

1

Reserved

1

Interleave

0

0

1

2

0

1

0

2

0

1

0

4

0

1

1

3

011

8

1

0

0

Reserved

100

Reserved

1

0

1

Reserved

101

Reserved

1

1

0

Reserved

110

Reserved

1

1

1

Reserved

111

Reserved