Security maintenance for programmable pacer reprogramming

Claim 1

A programmable, implantable body function control apparatus comprising: control means for influencing a function of the body by providing a train of stimulation pulses in accordance with a selected program, said control means including means for changing the selected program in order to vary at least one parameter of the stimulation pulses; program storage means for storing a predetermined number of bits representing the currently selected program and connected to said means for changing for supplying the currently selected program to said control means; program detection means connected to receive and temporarily store a predetermined number of bits representing a newly selected program, said detection means including output means connected to said program storage means for supplying the bits received by said detection means; signal conduction means connected to receive bit signals provided by a source outside the body and to supply a corresponding sequence of bits, representing such newly selected program, to said program detection means in a pattern independent of that of the train of stimulation pulses being provided by said control means; and program change enable means connected to said program storage means for supplying a program change signal which causes the bits temporarily stored in said detection means to be transferred into said program storage means to replace the bits previously stored in said program storage means, said program change enable means being composed of: first counter means connected for providing a count of the number of bits supplied to said program detection means, and for supplying a first enabling signal only when its count is equal to, and does not exceed, the predetermined number of bits; timer means connected for responding to the first bit supplied to said program detection means and for supplying a second enabling signal at the end of a given period of time after response to such first bit; synchronizing means connected to said control means for supplying a third enabling signal in synchronism with each stimulation pulse provided by said control means; and gating means connected to said counter means, said timer means and said synchronizing means for supplying such program change signal to said program storage means only when said first, second and third enabling signals are present in time coincidence, whereby the bits temporarily stored in said program detection means can be transferred into said program storage means only when precisely the predetermined number of bits has been supplied to said program detection means within the given period of time and at a point in time which is in synchronism with a stimulation pulse provided by said control means.