Designers of electric meters face the ongoing challenge of keeping system costs down. If the record-keeping portion of a system is tampered with, revenues collected from the end customer could be drastically reduced. To prevent the loss of billing data in the event of a power failure, this data is stored regularly into nonvolatile memory as often as once a minute or 525,600 writes per year. This means that a high-endurance memory such as an EEPROM or serial SRAM and a real-time clock that is accurate over temperature are required.
For reliable code and data storage, we offer a broad range of NOR Flash memory products including Parallel Flash, SPI, and Serial Quad I/O™ (SQI™). Supporting a variety of densities that can operate over wide voltage and temperature ranges and available in very small packages, these devices can meet the requirements of any metering application. SuperFlash® memory devices are cost-effective, nonvolatile memory data storage solutions that combine industry-leading features with fixed and fast program/erase times, ultra-low power consumption, high endurance and excellent reliability.
Serial EERAM is an easy, low-power and low-cost solution for implementing data logging and tamper detection in electric meters.
Memory Cell Structure
The MCP794xx and MCP795xxx low-power RTCC devices feature nonvolatile memory and can operate down to 1.3V through the backup supply connected to the VBAT input for timekeeping and SRAM retention only. As part of the power sense circuit, a time saver function is implemented to store the time when main power is lost and again when power is restored to log the time and duration of any power failure. A Watchdog Timer (WDT) is included for applications outside the microcontroller (MCU).
Accuracy is needed over a wide temperature range. These RTCC devices were implemented with digital trimming to support a software temperature-compensated design. In a design that uses an MCU and an external temperature sensor, the digital trimming registers can be updated with new calibration parameters when the temperature changes.
A 64-bit or 128-bit protected EEPROM space is available for a unique ID or MAC address to be programmed at the factory or by the end user.
To support anti-tampering requirements, two types of digital event detects are available in the MCP795xxx RTCC. One event detect input is high speed with a programmable pulse count that can identify the 1/4/16/32 pulses before sending an interrupt the MCU. The second event detect is low speed with a built-in debounce input filter to support noisy mechanical switches or the removal of a panel from the meter. Since the RTC is running all the time, the event detects operate all the time.