activating a mos transistor the impedance circuit 80 then conducts the operational mode signal from the operational mode voltage circuit 82 to the function circuit 78 by for example blowing an anti fuse or activating a mos transistor in response to the operational mode signal the function circuit 78 initiates an operational mode in the die 74 as described above thus the die 74 is fully testable even after being packaged in the ic module 68 and yet the test mode of the die 74 can be disabled as necessary so the ic module 68 can be used by end users in the field as shown in detail in fig6 b the switching circuit 76 of fig6 a may include a flash memory cell 77 programmed to activate or deactivate an nmos transistor 79 the cell 77 may be programmed for example to conduct the test mode initiate signal during a test mode and to isolate the bond pad 72 fig6 a from the function circuit 78 fig6 a during normal operations of the electronic system 60 fig6 a as shown in fig7 an inventive ic module 84 includes dice 86 having function circuits such as input buffers 88 selectively receiving a test mode initiate signal such as a supply voltage v cc through a first terminal 90 a dedicated conductor 92 and test mode enable bond pads 94 e g output enable oe bond pads it will be understood by those having skill in the field of this invention that the ic module 84 may be any electronic structure having at least one die accessed externally through terminals including for example an mcm such as a simm a dimm a ram card a ram module a rom card and a rom module it will also be.