Method to battery back up sdram data on power failure

Abstract

A system and method for providing battery back-up of SDRAM data upon power failure in which a power-down event is detected early and system hardware configures SDRAM self-refresh circuitry to set the SDRAM to a self refresh mode in which the SDRAM issues a single-refresh command just before system power drops below a safe threshold level and keeps the SDRAM in self-refresh mode after the system power drops by holding low a SDRAM clock enable signal using battery power. One embodiment for use with an external SDRAM controller includes a self-refresh control module (SRCM) and a battery backup module (BBUM). The BBUM includes power-down detection hardware and a battery for backing-up the SDRAM. In response to signals from the external SDRAM controller and the BBUM the self-refresh module generates SDRAM control signals for transitioning the SDRAM smoothly from normal mode to self-refresh mode during power-down events and vice-versa. The signals from the BBUM include an early power-down signal PDN that is asserted whenever power is about to go down. The signals from the external SDRAM controller include an auto-refresh signal that is asserted whenever the SDRAM controller initiates an auto-refresh operation.