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DS1345Y Datasheet(PDF) 2 Page - Maxim Integrated Products |
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DS1345Y Datasheet(HTML) 2 Page - Maxim Integrated Products |
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2 / 12 page  DS1345Y/AB 2 of 12 READ MODE The DS1345 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 17 address inputs (A0 – A16) defines which of the 131,072 bytes of data is to be 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 (Output Enable) 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 address access. WRITE MODE The DS1345 devices execute a write cycle whenever the WE and CE signals are in the active (low) state 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 DS1345AB provides full functional capability for VCC greater than 4.75V and write protects by 4.5V. The DS1345Y provides full functional capability for VCC greater than 4.5V and write protects by 4.25V. 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 2.7V, the power switching circuit connects the lithium energy source to RAM to retain data. During power-up, when VCC rises above approximately 2.7V, the power switching circuit connects external VCC to the RAM and disconnects the lithium energy source. Normal RAM operation can resume after VCC exceeds 4.75V for the DS1345AB and 4.5V for the DS1345Y. SYSTEM POWER MONITORING DS1345 devices have the ability to monitor the external VCC power supply. When an out-of-tolerance power supply condition is detected, the NV SRAMs warn a processor-based system of impending power failure by asserting RST . On power-up, RST is held active for 200ms nominal to prevent system operation during power-on transients and to allow tREC to elapse. RST has an open drain output driver. BATTERY MONITORING The DS1345 devices automatically perform periodic battery voltage monitoring on a 24-hour time interval. Such monitoring begins within tREC after VCC rises above VTP and is suspended when power failure occurs. After each 24-hour period has elapsed, the battery is connected to an internal 1M Ω=test resistor for one second. During this one second, if battery voltage falls below the battery voltage trip point (2.6V), the battery warning output BW is asserted. Once asserted, BW remains active until the module is replaced. The battery is still retested after each VCC power-up, however, even if BW is active. If the battery voltage is found to be higher than 2.6V during such testing, BW is de-asserted and regular 24-hour testing resumes. BW has an open drain output driver. |
Similar Part No. - DS1345Y |
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Similar Description - DS1345Y |
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