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M12S64322A-7BG Datasheet(PDF) 11 Page - Elite Semiconductor Memory Technology Inc. |
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M12S64322A-7BG Datasheet(HTML) 11 Page - Elite Semiconductor Memory Technology Inc. |
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11 / 46 page  ESMT M12S64322A Elite Semiconductor Memory Technology Inc. Publication Date: Mar. 2009 Revision: 1.1 11/46 DEVICE OPERATIONS CLOCK (CLK) The clock input is used as the reference for all SDRAM operations.All operations are synchronized to the positive going edge of the clock. The clock transitions must be monotonic between VIL and VIH. During operation with CKE high all inputs are assumed to be in valid state (low or high) for the duration of setup and hold time around positive edge of the clock for proper functionality and Icc specifications. CLOCK ENABLE(CKE) The clock enable (CKE) gates the clock onto SDRAM. If CKE goes low synchronously with clock (set-up and hold time same as other inputs), the internal clock suspended from the next clock cycle and the state of output and burst address is frozen as long as the CKE remains low. All other inputs are ignored from the next clock cycle after CKE goes low. When all banks are in the idle state and CKE goes low synchronously with clock, the SDRAM enters the power down mode from the next clock cycle. The SDRAM remains in the power down mode ignoring the other inputs as long as CKE remains low. The power down exit is synchronous as the internal clock is suspended. When CKE goes high at least “1CLK + tSS” before the high going edge of the clock, then the SDRAM becomes active from the same clock edge accepting all the input commands. BANK ADDRESSES (BA0~BA1) This SDRAM is organized as four independent banks of 524,288 words x 32 bits memory arrays. The BA0~BA1 inputs are latched at the time of assertion of RAS and CAS to select the bank to be used for the operation. The banks addressed BA0~BA1 are latched at bank active, read, write, mode register set and precharge operations. ADDRESS INPUTS (A0~A10) The 19 address bits are required to decode the 524,288 word locations are multiplexed into 11 address input pins (A0~A10). The 11 row addresses are latched along with RAS and BA0~BA1 during bank active command. The 8 bit column addresses are latched along with CAS , WE and BA0~BA1 during read or with command. NOP and DEVICE DESELECT When RAS , CAS and WE are high , The SDRAM performs no operation (NOP). NOP does not initiate any new operation, but is needed to complete operations which require more than single clock cycle like bank activate, burst read, auto refresh, etc. The device deselect is also a NOP and is entered by asserting CS high. CS high disables the command decoder so that RAS , CAS , WE and all the address inputs are ignored. POWER-UP 1.Apply power and start clock, Attempt to maintain CKE = “H”, DQM = “H” and the other pins are NOP condition at the inputs. 2.Maintain stable power, stable clock and NOP input condition for minimum of 200us. 3.Issue precharge commands for all banks of the devices. 4.Issue 2 or more auto-refresh commands. 5.Issue a mode register set command to initialize the mode register. cf.) Sequence of 4 & 5 is regardless of the order. The device is now ready for normal operation. MODE REGISTER SET (MRS) The mode register stores the data for controlling the various operating modes of SDRAM. It programs the CAS latency, burst type, burst length, test mode and various vendor specific options to make SDRAM useful for variety of different applications. The default value of the mode register is not defined, therefore the mode register must be written after power up to operate the SDRAM. The mode register is written by asserting low on CS , RAS , CAS and WE (The SDRAM should be in active mode with CKE already high prior to writing the mode register). The state of address pins A0~A10 and BA0~BA1 in the same cycle as CS , RAS , CAS and WE going low is the data written in the mode register. Two clock cycles is required to complete the write 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 into depending on functionality. The burst length field uses A0~A2, burst type uses A3, CAS latency (read latency from column address) use A4~A6, vendor specific options or test mode use A7~A8, A10/AP and BA0~BA1, A7~A9, A10/AP and BA0~BA1 must be set to low for normal SDRAM operation. Refer to the table for specific codes for various burst length, burst type and CAS latencies. BANK ACTIVATE The bank activate command is used to select a random row in an idle bank. By asserting low on RAS and CS with desired row and bank address, a row access is initiated. The read or write operation can occur after a time delay of tRCD (min) from the time of bank activation. tRCD is the internal timing parameter of SDRAM, therefore it is dependent on operating clock frequency. The minimum number of clock cycles required between bank activate and read or write command should be calculated by dividing tRCD (min) with cycle time of the clock and then rounding of the result to the next higher integer. |
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