To program a fire mode to each selector position you would adjust the S1 and S2 settings in your FCU programing menu. On most common rifles such as an M4, the S1 is your semi auto selector position and S2 is your full auto selector position. By default the S1 should be set to S101 for Semi Auto, and the S2 should be set to S200 for full auto. Changing the number will change the fire mode set to that selector position.00 = Full Auto, 01 = Semi Auto, 02 = 2 Round Burst, 03 = 3 Round Burst, etc. on up to 09 = 9 Round Burst.