EtronTech
EM68932DVKA
z 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 pins A0~A11 and BA0, BA1 in the same cycle in which
,
,
CS RAS
are asserted Low is written into the Mode Register. A minimum of two clock cycles, tMRD, are
WE
and
CAS
required to complete the write 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 Latency (read latency
CAS
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
latencies.
CAS
Table 4. Mode Register Bitmap
BA1 BA0 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 Address Field
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
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Reserved
Reserved
2
0 Sequential
Interleave
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Reserved
2
1
4
3
8
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
Reserved
CK
CK
PRE
ALL
Any
Command
NOP
NOP
NOP
MRS*1
NOP
NOP
NOP
Command
*2
tMRD= 2*tCK
tRP
*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.
Don’t Care
Figure 3.Mode Register Set Cycle
Etron Confidential
7
Rev. 1.0
Mar. 2009
ETRON [ ETRON TECHNOLOGY, INC. ]
