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STK12C68-SF35ITR Datasheet(PDF) 10 Page - Simtek Corporation |
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STK12C68-SF35ITR Datasheet(HTML) 10 Page - Simtek Corporation |
10 / 20 page 10 February 2007 Document Control #ML0008 Rev 0.7 STK12C68 (SMD5962-94599) + 1 14 28 27 26 15 1 14 28 27 26 15 1 14 28 27 26 15 Figure 2. AutoStore Mode Figure 3. System Power Mode Figure 4. AutoStore Inhibit Mode 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 0000 (hex) Valid READ 2. Read address 1555 (hex) Valid READ 3. Read address 0AAA (hex) Valid READ 4. Read address 1FFF (hex) Valid READ 5. Read address 10F0 (hex) Valid READ 6. Read address 0F0E (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 OPERATION The STK12C68 can be powered in one of three modes. During normal AutoStore operation, the STK12C68 will draw current from V CCX to charge a capacitor connected to the V CAP pin. This stored charge will be used by the chip to perform a single STORE opera- tion. After power up, when the voltage on the V CAP pin drops below V SWITCH, the part will automatically disconnect the V CAP pin from VCCX 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 (Figure 3), both V CCX and VCAP are connected to the + 5V power supply without the 68 μF capacitor. In this mode the AutoStore function of the STK12C68 will operate on the stored system charge as power goes down. The user must, how- ever, guarantee that V CCX does not drop below 3.6V during the 10ms STORE cycle. If an automatic STORE on power loss is not required, then V CCX can be tied to ground and + 5V applied to V CAP (Figure 4). This is the AutoStore Inhibit mode, in which the AutoStore function is disabled. If the STK12C68 is operated in this configuration, refer- ences to V CCX should be changed to VCAP throughout this data sheet. In this mode, STORE operations may be triggered through software control or the HSB pin. It is not permissible to change between these three options “on the fly.” 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 initi- ated STORE cycles are performed regardless of whether a WRITE operation has taken place. An optional pull-up resistor is shown connected to HSB. This can be used to signal the system that the AutoStore cycle is in progress. If the power supply drops faster than 20 μs/volt before V CCX reaches VSWITCH, then a 2.2 ohm resistor should be inserted between V CCX and the system supply to avoid momentary excess of current between Vccx and Vcap. |
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