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STK14C88-NF35U Datasheet(PDF) 10 Page - Simtek Corporation |
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STK14C88-NF35U Datasheet(HTML) 10 Page - Simtek Corporation |
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10 / 15 page  10 Feb, 2008 Document Control #ML0066 Rev 2.0 STK14C88-NF35U SOFTWARE NONVOLATILE RECALL A software RECALL cycle is initiated with a sequence of READ operations in a manner similar to the soft- ware STORE initiation. To initiate the RECALL cycle, the following sequence of E controlled READ opera- tions must be performed: 1. Read address 0E38 (hex) Valid READ 2. Read address 31C7 (hex) Valid READ 3. Read address 03E0 (hex) Valid READ 4. Read address 3C1F (hex) Valid READ 5. Read address 303F (hex) Valid READ 6. Read address 0C63 (hex) Initiate RECALL cycle Internally, RECALL is a two-step procedure. First, the SRAM data is cleared, and second, the nonvolatile information is transferred into the SRAM cells. After the t RECALL cycle time the SRAM will once again be ready for READ and WRITE operations. The RECALL operation in no way alters the data in the nonvolatile elements. The nonvolatile data can be recalled an unlimited number of times. AutoStore MODE The STK14C88-NF35U can be powered in one of three modes. During normal AutoStore operation, the STK14C88- NF35U will draw current from V CC to charge a capac- itor connected to the V CAP pin. This stored charge will be used by the chip to perform a single STORE operation. After power up, when the voltage on the V CAP pin drops below VSWITCH, the part will automati- cally disconnect the V CAP pin from VCC and initiate a STORE operation. Figure 2 shows the proper connection of capacitors for automatic store operation. A charge storage capacitor having a capacity of between 68 μF and 220 μF (± 20%) rated at 6V should be provided. In system power mode, both V CC and VCAP are con- nected to the + 5V power supply without the 68 μF capacitor. In this mode the AutoStore function of the STK14C88-NF35U will operate on the stored sys- tem charge as power goes down. The user must, however, guarantee that V CC does not drop below 3.6V during the 10ms STORE cycle. In order to prevent unneeded STORE operations, automatic STOREs as well as those initiated by externally driving HSB low will be 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. If the power supply drops faster than 20 μs/volt before V CC reaches VSWITCH, then a 2.2 ohm resistor should be inserted between the V CC pin on the IC and the system supply to avoid momentary excess of current between Vcc and Vcap. AutoStore INHIBIT MODE If an automatic STORE on power loss is not required, then Vcc can be tied to ground and system power applied to VCAP (Figure 3). This is the AutoStore Inhibit mode, in which the AutoStore func- tion is disabled. If the STK14C88-NF35U is oper- ated in this configuration, references to Vcc should be changed to VCAP throughout this data sheet. In this mode, STORE operations may be triggered through software control. It is not permissible to change between these three options “on the fly.” Figure 2: AutoStore Mode 1 16 32 31 17 30 + 10k Ω∗ Figure 3: AutoStore Inhibit Mode 1 16 32 31 17 30 *If HSB is not used, it should be left unconnected. |
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