ESMT
M13S32321A (2G)
Mode Register Definition
Mode Register Set (MRS)
The mode register stores the data for controlling the various operating modes of DDR SDRAM. It programs CAS latency,
addressing mode, burst length, test mode, DLL reset and various vendor specific options to make DDR SDRAM useful for variety of
different applications. The default value of the register is not defined, therefore the mode register must be written after EMRS setting
for proper DDR SDRAM operation. The mode register is written by asserting low on CS , RAS , CAS , WE and BA (The DDR
SDRAM should be in all bank precharge with CKE already high prior to writing into the mode register). The state of address pins
A0~A10 in the same cycle as CS , RAS , CAS , WE and BA going low is written in the mode register. Two clock cycles are
requested to complete the write operation in the mode register. The mode register contents can be changed using the same
command and clock cycle requirements during operation as long as all banks are in the idle state. The mode register is divided into
various fields depending on functionality. The burst length uses A0~A2, addressing mode uses A3, CAS latency (read latency from
column address) uses A4~A6. A7 is used for test mode. A8 is used for DLL reset. A7 must be set to low for normal MRS operation.
Refer to the table for specific codes for various burst length, addressing modes and CAS latencies.
BA
A10
A9
A8
A7
A6
A5
A4
A3
BT
A2
A1
A0
Address Bus
DLL
Burst Length
Mode Register
0
RFU
TM
CAS Latency
A8
DLL Reset
No
A7
Mode
Normal
Test
A3
0
Burst Type
Sequential
Interleave
0
1
0
1
Yes
1
Burst Length
Length
CAS Latency
A2
A1
A0
A6
0
A5
0
A4
0
Latency
Sequential Interleave
BA
0
Operating Mode
MRS Cycle
Reserve
Reserve
2
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
Reserve
2
Reserve
2
0
0
1
1
EMRS Cycle
0
1
0
4
4
0
1
1
3
8
8
1
0
0
Reserve
Reserve
2.5
Reserve
Reserve
Reserve
Reserve
Reserve
Reserve
Reserve
Reserve
1
0
1
1
1
0
1
1
1
Reserve
Note: RFU (Reserved for future use) must stay “0” during MRS cycle.
Elite Semiconductor Memory Technology Inc.
Publication Date : Aug. 2012
Revision : 1.0 14/48
ESMT [ ELITE SEMICONDUCTOR MEMORY TECHNOLOGY INC. ]
