Data protection system in a data processing system

Abstract

A data protection system for protecting data stored in a memory in a data processing system having at least a channel system, a device controller and an external storage device. The data protection system includes a memory provided in the device controller which receives a power source voltage, and temporarily stores data to be transferred. A battery is connected to the power source and the memory, is charged by the power source when the power source is normal, and supplies a battery voltage to the memory when the power source is accidentally interrupted. A first voltage check circuit is connected to the battery, compares the battery voltage with a first reference voltage, and generates a battery error signal when the battery voltage is lower than the first reference voltage. A second voltage check circuit is connected to the battery; compares the battery voltage with a second reference voltage and generates a battery charging signal when the battery voltage lies between the first and second reference voltages. A control circuit selectively determines two modes-one mode being a write-back mode for transferring data from the memory to the external storage device after data is stored in the memory, and the other being a write-through mode for directly transferring data from the channel system directly to the external storage device when one or both of the battery error signal and the battery charging signal is input thereto.