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AS4C128M8D2 Datasheet(PDF) 9 Page - Alliance Semiconductor Corporation |
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AS4C128M8D2 Datasheet(HTML) 9 Page - Alliance Semiconductor Corporation |
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9 / 59 page  AS4C128M8D2 Alliance Memory Inc. 551 Taylor Way, San Carlos, CA 94070 TEL: (650) 610-6800 FAX: (650) 620-9211 Alliance Memory Inc. reserves the right to change products or specification without notice. 9 Rev. 1.0 June 2013 Mode Register Set(MRS) The mode register stores the data for controlling the various operating modes of DDR2 SDRAM. It controls CAS latency, burst length, burst sequence, test mode, DLL reset, WR, and various vendor specific options to make DDR2 SDRAM useful for various applications.The default value of the mode register is not defined, therefore the mode register must be programmed during initialization for proper operation. The mode register is written by asserting LOW on CS#, RAS#, CAS#, WE#, BA0 and BA1, while controlling the state of address pins A0 - A13. The DDR2 SDRAM should be in all bank precharge state with CKE already HIGH prior to writing into the mode register.The mode register set command cycle time (tMRD) is required to complete the write operation to the mode register. The mode register contents can be changed using the same command and clock cycle requirements during normal operation as long as all bank are in the precharge state.The mode register is divided into various fields depending on functionality. - Burst Length Field (A2, A1, A0) : This field specifies the data length of column access and selects the Burst Length. - Addressing Mode Select Field (A3) : The Addressing Mode can be Interleave Mode or Sequential Mode. Both Sequential Mode and Interleave Mode support burst length of 4 and 8. - CAS Latency Field (A6, A5, A4) : This field specifies the number of clock cycles from the assertion of the Read command to the first read data. The minimum whole value of CAS Latency depends on the frequency of CK. The minimum whole value satisfying the following formula must be programmed into this field. (tCAC(min) ≦ CAS Latency X tCK) - Test Mode Field (A7); DLL Reset Mode Field (A8) : These two bits must be programmed to "00" in normal operation. - Write recovery Field (A11, A10, A9) : The WR register is used by the DDR2 SDRAM during WRITE with auto precharge operation. The WR register is used by the DDR2 SDRAM during WRITE with auto precharge operation. - Active Power down Field (A12) : PD mode enables the user to determine the active power-down mode, which determines performance versus power savings. oes not apply to precharge PD mode. - (BA0-BA1): Bank addresses to define MRS selection. Table 5. Mode Register Bitmap BA2 BA1 BA0 A13 A12 A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 Address Field 0 *2 0 0 0 *2 PD WR DLL TM CAS Latency BT Burst Length Mode Register A8 DLL Reset A7 Mode A3 Burst Type A2 A1 A0 BL 0 No 0 Normal 0 Sequential 0 1 0 4 1 Yes 1 Test 1 Interleave 0 1 1 8 NOTE 1: For DDR2-800, WR min is determined by tCK (avg) max and WR max is determined by tCK(avg) min. WR [cycles] = RU {tWR[ns]/tCK(avg)[ns]}, where RU stands for round up. The mode register must be programmed to this value.This is also used with tRP to determine tDAL. NOTE 2: BA2 and A13 are reserved for future use and must be set to 0 when programming the MR. A12 Active power down exit time Write recovery for autoprecharge *1 0 Fast exit (use tXARD) A11 A10 A9 WR(cycles) A6 A5 A4 CAS Latency 1 Slow exit (use tXARDS) 0 0 0 Reserved 0 0 0 Reserved 0 0 1 2 0 0 1 Reserved BA1 BA0 MRS Mode 0 1 0 3 0 1 0 Reserved 0 0 MR 0 1 1 4 0 1 1 3 0 1 EMR(1) 1 0 0 5 1 0 0 4 1 0 EMR(2) 1 0 1 6 1 0 1 5 1 1 EMR(3) 1 1 0 Reserved 1 1 0 6 1 1 1 Reserved 1 1 1 Reserved |
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