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CY14B108N-ZSP45XI Datasheet(PDF) 5 Page - Cypress Semiconductor |
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CY14B108N-ZSP45XI Datasheet(HTML) 5 Page - Cypress Semiconductor |
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5 / 24 page  CY14B108L CY14B108N Document #: 001-45523 Rev. *I Page 5 of 24 Device Operation The CY14B108L/CY14B108N nvSRAM is made up of two functional components paired in the same physical cell. They are a SRAM memory cell and a nonvolatile QuantumTrap cell. The SRAM memory cell operates as a standard fast static RAM. Data in the SRAM is transferred to the nonvolatile cell (the STORE operation), or from the nonvolatile cell to the SRAM (the RECALL operation). Using this unique architecture, all cells are stored and recalled in parallel. During the STORE and RECALL operations, SRAM read and write operations are inhibited. The CY14B108L/CY14B108N supports infinite reads and writes similar to a typical SRAM. In addition, it provides infinite RECALL operations from the nonvolatile cells and up to 1 million STORE operations. See the “Truth Table For SRAM Operations” on page 17 for a complete description of read and write modes. SRAM Read The CY14B108L/CY14B108N performs a read cycle when CE and OE are LOW and WE and HSB are HIGH. The address specified on pins A0-19 or A0-18 determines which of the 1,048,576 data bytes or 524,288 words of 16 bits each are accessed. Byte enables (BHE, BLE) determine which bytes are enabled to the output, in the case of 16-bit words. When the read is initiated by an address transition, the outputs are valid after a delay of tAA (read cycle 1). If the read is initiated by CE or OE, the outputs are valid at tACE or at tDOE, whichever is later (read cycle 2). The data output repeatedly responds to address changes within the tAA access time without the need for transi- tions on any control input pins. This remains valid until another address change or until CE or OE is brought HIGH, or WE or HSB is brought LOW. SRAM Write A write cycle is performed when CE and WE are LOW and HSB is HIGH. The address inputs must be stable before entering the write cycle and must remain stable until CE or WE goes HIGH at the end of the cycle. The data on the common I/O pins DQ0–15 are written into the memory if the data is valid tSD before the end of a WE controlled write or before the end of an CE controlled write. The Byte Enable inputs (BHE, BLE) determine which bytes are written, in the case of 16-bit words. Keep OE HIGH during the entire write cycle to avoid data bus contention on common I/O lines. If OE is left LOW, internal circuitry turns off the output buffers tHZWE after WE goes LOW. AutoStore Operation The CY14B108L/CY14B108N stores data to the nvSRAM using one of the following three storage operations: Hardware STORE activated by the HSB; Software STORE activated by an address sequence; AutoStore on device power-down. The AutoStore operation is a unique feature of QuantumTrap technology and is enabled by default on the CY14B108L/CY14B108N. During a normal operation, the device draws current from VCC to charge a capacitor connected to the VCAP pin. This stored charge is used by the chip to perform a single STORE operation. If the voltage on the VCC pin drops below VSWITCH, the part automatically disconnects the VCAP pin from VCC. A STORE operation is initiated with power provided by the VCAP capacitor. Note If the capacitor is not connected to VCAP pin, AutoStore must be disabled using the soft sequence specified in Preventing AutoStore on page 8. In case AutoStore is enabled without a capacitor on VCAP pin, the device attempts an AutoStore operation without sufficient charge to complete the Store. This corrupts the data stored in nvSRAM. Figure 3 shows the proper connection of the storage capacitor (VCAP) for automatic STORE operation. Refer to DC Electrical Characteristics on page 9 for the size of VCAP. The voltage on the VCAP pin is driven to VCC by a regulator on the chip. A pull-up should be placed on WE to hold it inactive during power-up. This pull-up is effective only if the WE signal is tristate during power-up. Many MPUs tristate their controls on power-up. This should be verified when using the pull-up. When the nvSRAM comes out of power-on-RECALL, the MPU must be active or the WE held inactive until the MPU comes out of reset. To reduce unnecessary nonvolatile STOREs, AutoStore and Hardware STORE operations are ignored unless at least one write operation has taken place since the most recent STORE or RECALL cycle. Software initiated STORE cycles are performed regardless of whether a write operation has taken place. The HSB signal is monitored by the system to detect if an AutoStore cycle is in progress. Figure 3. AutoStore Mode Hardware STORE Operation The CY14B108L/CY14B108N provides the HSB pin to control and acknowledge the STORE operations. Use the HSB pin to request a Hardware STORE cycle. When the HSB pin is driven LOW, the CY14B108L/CY14B108N conditionally initiates a STORE operation after tDELAY. An actual STORE cycle only begins if a write to the SRAM has taken place since the last STORE or RECALL cycle. The HSB pin also acts as an open drain driver (internal 100 k Ω weak pull-up resistor) that is inter- nally driven LOW to indicate a busy condition when the STORE (initiated by any means) is in progress. Note After each Hardware and Software STORE operation HSB is driven HIGH for a short time (tHHHD) with standard output high current and then remains HIGH by internal 100 k Ω pull-up resistor. 0.1 uF VCC VCAP WE VCAP VSS VCC [+] Feedback |
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