System and method for electrically isolating a device from higher voltage devices

Abstract

An isolation system and method that electrically couples a device to a bus during cycles associated with or accessing the device, but otherwise isolates the device from the bus. The isolation system includes an isolation device coupled to the device and to the bus that includes an enable input adapted to receive an enable signal, where the isolation device electrically couples the device to said bus while the enable signal is asserted, but otherwise electrically isolates the device from the bus. The isolation system further includes enable logic that detects cycles on the bus and provides the enable signal to the enable input of the isolation device during a cycle if the cycle is associated with the device. The isolation device may comprise a bus switch, one or more discrete isolating devices such as bipolar transistors, field-effect transistors, or any other suitable device for isolating a device from the bus. Generally, the enable logic may comprise decode logic that decodes an address on the bus during the bus cycle to determine if the address corresponds to an address of the device. Decode logic is usefuil for decoding a memory cycle on the bus for accessing a low voltage memory device, which is otherwise isolated from the bus.