DS1644-120 Nonvolatile Timekeeping RAM 120ns PDIP-28

Description

DS1644-120 Nonvolatile Timekeeping RAM 120ns PDIP-28 The DS1644-120 Nonvolatile Timekeeping RAM 120ns PDIP-28 is a DIP-28 module that combines 32K×8 nonvolatile static RAM with a fully functional, factory-calibrated real-time clock and an integrated crystal plus lithium energy source for autonomous timekeeping and data retention during power loss. The device presents clock registers in the top eight RAM locations, uses a double-buffered update scheme to prevent corrupted reads during time updates, and implements power-fail circuitry that switches to the internal energy source and disables writes when VCC falls below the write-protection threshold to preserve stored data and clock integrity. Features Integrated NV-SRAM, real-time clock, crystal, power-fail control circuit and lithium energy source for unattended timekeeping and data retention. 32K×8 byte-wide nonvolatile static RAM accessible via standard address/data bus locations. Real-time clock registers stored in the eight top RAM locations and updated in 24-hour BCD with leap-year compensation valid to 2100. Double-buffered clock registers to avoid incorrect reads during clock updates and to prevent time loss during access cycles. Totally nonvolatile with over 10 years of data retention when the oscillator is enabled. Fast access time tailored to the -120 variant: 120ns read/write cycle performance. Power-fail write protection and a PFO (power-fail output) to signal imminent loss of VCC and to prevent unsafe writes. PINOUT Pin Function A0–A14 Address Input CE Chip Enable OE Output Enable WE Write Enable VCC +5 Volts GND Ground DQ0–DQ7 Data Input/Output Specifications Parameter Value Memory Organization 32K×8 Access Time 120ns Supply Voltage 5.0V±10% Write Protection Voltage (VPF) 4.0–4.5V (typ4.25V) Average VCC Current (active) ≤75mA Standby Current (TTL standby) ≤6mA Logic Levels VIH≥2.2V, VIL≤0.8V Address Lines A0–A14 Data Bus DQ0–DQ7 (bidirectional) RTC Registers Top 8 RAM locations (BCD year,month,date,day,hour,minute,second). Data Retention 10years (oscillator on) Operating Temperature 0°C to 70°C Storage Temperature −20°C to +70°C Absolute Pin Voltage Range −0.3V to +7.0V Package 28-pin PDIP module (integrated crystal & lithium energy source) Soldering Temperature 260°C for 10s Applications Nonvolatile program or data storage with on-board timekeeping for embedded systems. RTC plus RAM for industrial controllers, data-loggers and metering equipment. Replacement or retrofit of legacy systems requiring DIP-28 timekeeping SRAM. Battery-backed memory for POS terminals, vending machines and security/access devices. Portable or off-grid devices that require autonomous clocking and guaranteed data retention. Package Contents 1x DS1644-120 Nonvolatile Timekeeping RAM 120ns PDIP-28. Documents Datasheet DS1644-120

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