code is then changed to a trinary code having values 0 1 and 2 and the initial trinary rolling code is set to 0 it may be appreciated that it is trinary code which is actually used to modify the radio frequency oscillator signal and the trinary code is best seen in fig6 it may be noted that the bit timing in fig6 for a 0 is 1 5 milliseconds down time and 0 5 millisecond up time for a 1 1 millisecond down and 1 millisecond up and for a 2 0 5 millisecond down and 1 5 milliseconds up the up time is actually the active time when carrier is being generated the down time is inactive when the carrier is cut off the codes are assembled in two frames each of 20 trinary bits with the first frame being identified by a 0 5 millisecond sync bit and the second frame being identified by a 1 5 millisecond sync bit in a step 510 the next highest power of 3 is subtracted from the rolling code and a test is made in a step 512 to determine if the result is greater than zero if it is the next most significant digit of the binary rolling code is incremented in a step 514 following which flow is returned to the step 510 if the result is not greater than 0 the next highest power of 3 is added to the rolling code in the step 516 in the step 518 another highest power of 3 is incremented and in a step 520 a test is determined as to whether the rolling code is completed if it is not control is transferred back.