a controller for a line regulation device such as a voltage regulator is provided with an interface to a removable memory module . the memory module is preferably of the memory card type which can be carried by a field engineer in a clothing pocket . when the memory card is inserted into an externally accessible slot in the controller , its presence is signaled to the controllers microprocessor . in response , the microprocessor reads user selected control parameters which are entered via the controller &# 39 ; s front panel . depending on the control parameters , the microprocessor updates the programming code in its internal memory , executes the code stored in the memory card while it is present but does not update its internal memory , or dumps selected status information to the memory card so that it can be analyzed at a different location .