Non-volatile SRAM DS1747

The DS1747 is a full-featured, year 2000-compliant (Y2KC) real-time clock/calendar (RTC) and 512k x 8 nonvolatile SRAM. All registers within the DS1747 are accessible to the user through a single-byte wide interface as shown in Figure 1. The RTC information and control bits occupy the highest 8 addresses in the RAM. The RTC registers contain century, year, month, day, weekday, hour, minute, and second data in 24-hour BCD format. The device automatically performs date correction for each month and leap year. The RTC clock registers are double buffered to prevent access to incorrect data during the clock update cycle. The double buffer system also prevents time loss caused by undecremented countdowns when accessing the time registers. The DS1747 also contains power-fail circuitry to disable the device when the VCC supply is out of tolerance. This feature prevents data loss in situations where low VCC can cause unpredictable system operation, thereby preventing erroneous accesses and updates.

Key Features

Integrated NV SRAM, real-time clock (RTC), crystal, power-fail control circuit and lithium battery

The clock registers are accessed in exactly the same way as static RAM. These registers are located at the highest 8 addresses in the RAM.

Century byte register; Y2K compliant

Completely non-volatile, can operate for more than 10 years without power

BCD-coded century, year, month, day, weekday, hour, minute and second data with automatic leap year compensation up to 2100

Battery voltage indicator

Power-fail write protection, allowing ±10% VCC supply tolerance

The lithium battery is in open circuit freshness mode until the first power is applied

For DIP modules only:

Standard JEDEC byte width 512k x 8 static RAM pinout

For PowerCap templates only:

Surface-mountable package connects directly to PowerCap containing battery and crystal

Replaceable battery (PowerCap)

Power-on reset output

Pin-Compatible with Other Density DS174xP Timekeeping RAMs

Chips available in industrial temperature range (-40°C to +85°C)