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FM20L08 Datasheet(PDF) 4 Page - Ramtron International Corporation |
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FM20L08 Datasheet(HTML) 4 Page - Ramtron International Corporation |
4 / 14 page FM20L08 - Industrial Temp. Rev. 1.72 May 2007 Page 4 of 14 Overview The FM20L08 is a bytewide FRAM memory logically organized as 131,072 x 8 and is accessed using an industry standard parallel interface. All data written to the part is immediately nonvolatile with no delay. The device offers page mode operation which provides higher speed access to addresses within a page (row). An access to a different page requires that either /CE transitions low or the upper address A(16:3) changes. Memory Operation Users access 131,072 memory locations with 8 data bits each through a parallel interface. The FRAM array is organized as 8 blocks each having 2048 rows. Each row has 8 column locations, which allows fast access in page mode operation. Once an initial address has been latched by the falling edge of /CE, subsequent column locations may be accessed without the need to toggle /CE. When /CE is deasserted high, a precharge operation begins. Writes occur immediately at the end of the access with no delay. The /WE pin must be toggled for each write operation. Read Operation A read operation begins on the falling edge of /CE. The falling edge of /CE causes the address to be latched and starts a memory read cycle if /WE is high. Data becomes available on the bus after the access time has been satisfied. Once the address has been latched and the access completed, a new access to a random location (different row) may begin while /CE is still low. The minimum cycle time for random addresses is tRC. Note that unlike SRAMs, the FM20L08’s /CE-initiated access time is faster than the address cycle time. The FM20L08 will drive the data bus only when /OE is asserted low and the memory access time has been satisfied. If /OE is asserted prior to completion of the memory access, the data bus will not be driven until valid data is available. This feature minimizes supply current in the system by eliminating transients caused by invalid data being driven onto the bus. When /OE is inactive, the data bus will remain hi-Z. Write Operation Writes occur in the FM20L08 in the same time interval as reads. The FM20L08 supports both /CE- and /WE-controlled write cycles. In both cases, the address is latched on the falling edge of /CE. In a /CE-controlled write, the /WE signal is asserted prior to beginning the memory cycle. That is, /WE is low when /CE falls. In this case, the device begins the memory cycle as a write. The FM20L08 will not drive the data bus regardless of the state of /OE as long as /WE is low. Input data must be valid when /CE is deasserted high. In a /WE-controlled write, the memory cycle begins on the falling edge of /CE. The /WE signal falls some time later. Therefore, the memory cycle begins as a read. The data bus will be driven if /OE is low, however it will hi-Z once /WE is asserted low. The /CE- and /WE-controlled write timing cases are shown on page 11. In the Write Cycle Timing 2 diagram, the data bus is shown as a hi-Z condition while the chip is write-enabled and before the required setup time. Although this is drawn to look like a mid-level voltage, it is recommended that all DQ pins comply with the minimum VIH/VIL operating levels. Write access to the array begins on the falling edge of /WE after the memory cycle is initiated. The write access terminates on the rising edge of /WE or /CE, whichever comes first. A valid write operation requires the user to meet the access time specification prior to deasserting /WE or /CE. Data setup time indicates the interval during which data cannot change prior to the end of the write access (/WE or /CE high). Unlike other truly nonvolatile memory technologies, there is no write delay with FRAM. Since the read and write access times of the underlying memory are the same, the user experiences no delay through the bus. The entire memory operation occurs in a single bus cycle. Data polling, a technique used with EEPROMs to determine if a write is complete, is unnecessary. Page Mode Operation The FM20L08 provides the user fast access to any data within a row element. Each row has eight column locations. An access can start anywhere within a row and other column locations may be accessed without the need to toggle the /CE pin. For page mode reads, once the first data byte is driven onto the bus, the column address inputs A(2:0) may be changed to a new value. A new data byte is then driven to the DQ pins. For page mode writes, the first write pulse defines the first write access. While /CE is low, a subsequent write pulse along with a new column address provides a page mode write access. Precharge Operation The precharge operation is an internal condition in which the state of the memory is prepared for a new access. Precharge is user-initiated by driving the /CE signal high. It must remain high for at least the minimum precharge time tPC. |
Número de pieza similar - FM20L08_07 |
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Descripción similar - FM20L08_07 |
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