Method and apparatus for accessing a nonvolatile memory

Abstract

A method and apparatus for accessing a nonvolatile electrically erasable programmable read only memory (EEPROM) following hermetic closure of a device containing the EEPROM. The EEPROM is accessed by a direct connection to a feedthrough pin extending through the hermetic enclosure. Following hermetic sealing, the memory is still accessible for programming. In the implantable medical device field, the invention may be utilized to program in the device serial number or similar data which may be telemetered out of the device on command of an external programmer/transciever in order to identify the device. In a specific application, a rate responsive pacemaker, an activity sensor mounted within the hermetically sealed enclosure is electrically connected to the EEPROM and other operating circuitry. At final test, the output of the activity sensor may be checked against specific levels of mechanical activity input applied to the exterior of the enclosure by observing the pacing rates developed from the sensor signal values, calculating a gain factor and storing the gain factor(s) in the EEPROM for adjusting the activity sensor derived pacing rate through its normal range of response. This trimming of the response of the activity sensor minimizes the number of completed medical devices that fail to meet specification tolerances and allows those tolerances to be narrowed to assure relatively consistent variations in pacing rate as a function of applied mechanical force. Once the factor(s) is stored and its accuracy is confirmed by retesting the pacing rate, the dedicated feedthrough pin is removed or rendered inaccessible.