AS4C256M16D3
Mode Register MR2
The Mode Register MR2 stores the data for controlling refresh related features, Rtt_WR impedance, and CAS
write latency. The Mode Register 2 is written by asserting low on CS#, RAS#, CAS#, WE#, high on BA1 and low
on BA0 and BA2, while controlling the states of address pins according to the table below.
Table 7. Extended Mode Register EMR (2) Bitmap
BA2 BA1 BA0 A14 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 Address Field
0*1
1
0
0*1
Rtt_WR
0*1 SRT ASR
CWL
PASR
Mode Register (2)
BA1 BA0 MRS mode
A6
0
Auto Self-Refresh (ASR)
Manual SR Reference (SRT)
ASR enable (Optional)
0
0
1
1
0
1
0
1
MR0
MR1
MR2
MR3
1
A10 A9
RTT_WR *2
A2 A1 A0 Partial Array Self-Refresh (Optional)
Dynamic ODT off (Write does not affect Rtt value)
0
0
1
1
0
1
0
1
RZQ/4
RZQ/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
Full Array
Half Array (BA[2:0]=000,001,010,&011)
Quarter Array (BA[2:0]=000,&001)
1/8th Array (BA[2:0]=000)
Reserved
3/4 Array (BA[2:0]=010,011,100.101,110,&111)
Half Array (BA[2:0]=100,101,110,&111)
Quarter Array (BA[2:0]=110,&111)
1/8th Array (BA[2:0]=111)
Self-Refresh Temperature (SRT) Range
Normal operating temperature range
A7
A5 A4 A3
CAS write Latency (CWL)
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
5 (tCK(avg)≧2.5ns)
0
1
Extended (optional) operating temperature range
6 (2.5ns＞tCK(avg)≧1.875ns)
7 (1.875ns＞tCK(avg)≧1.5ns)
8 (1.5ns＞tCK(avg)≧1.25ns)
Reserved
Reserved
Reserved
Reserved
Note 1:
Note 2:
BA2 and A8, A11~ A14 are RFU and must be programmed to 0 during MRS.
The Rtt_WR value can be applied during writes even when Rtt_Nom is disabled.
During write leveling, Dynamic ODT is not available.
Confidential
18
Rev. 3.0
Aug. /2014
ALSC [ ALLIANCE SEMICONDUCTOR CORPORATION ]
