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DS1265W Datasheet(PDF) 2 Page - Dallas Semiconductor |
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DS1265W Datasheet(HTML) 2 Page - Dallas Semiconductor |
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2 / 8 page  DS1265W 2 of 8 READ MODE The DS1265 devices execute a read cycle whenever WE (Write Enable) is inactive (high) and CE (Chip Enable) and OE (Output Enable) are active (low). The unique address specified by the 20 address inputs (A0–A19) defines which of the 1,048,576 bytes of data is accessed. Valid data will be available to the eight data output drivers within tACC (Access Time) after the last address input signal is stable, providing that CE and OE access times are also satisfied. If OE and CE access times are not satisfied, then data access must be measured from the later-occurring signal ( CE or OE ) and the limiting parameter is either tCO for CE or tOE for OE rather than tACC. WRITE MODE The DS1265 devices execute a write cycle whenever WE and CE signals are active (low) after address inputs are stable. The later-occurring falling edge of CE or WE will determine the start of the write cycle. The write cycle is terminated by the earlier rising edge of CE or WE . All address inputs must be kept valid throughout the write cycle. WE must return to the high state for a minimum recovery time (tWR) before another cycle can be initiated. The OE control signal should be kept inactive (high) during write cycles to avoid bus contention. However, if the output drivers are enabled ( CE and OE active), then WE will disable the outputs in tODW from its falling edge. DATA-RETENTION MODE The DS1265W provides full functional capability for VCC greater than 3.0V and write protects by 2.8V. Data is maintained in the absence of VCC without any additional support circuitry. The nonvolatile static RAMs constantly monitor VCC. Should the supply voltage decay, the NV SRAMs automatically write protect themselves, all inputs become “don’t care,” and all outputs become high-impedance. As VCC falls below approximately 2.5V, a power-switching circuit connects the lithium energy source to RAM to retain data. During power-up, when VCC rises above approximately 2.5V, the power-switching circuit connects external VCC to RAM and disconnects the lithium energy source. Normal RAM operation can resume after VCC exceeds 3.0V. FRESHNESS SEAL Each DS1265 device is shipped from Dallas Semiconductor with its lithium energy source disconnected, guaranteeing full energy capacity. When VCC is first applied at a level greater than VTP, the lithium energy source is enabled for battery backup operation. |
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