Two LFSRs are constructed per the GPS ICD, and the first is added to selected taps of the second to produce the selected final PRN sequence.
With io_in[2:7] set to 2 to select PRN2, reset and then drive the clock; the output sequence on io_out[2] will start with 1, 1, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1.
| # | Input | Output |
|---|---|---|
| 0 | clock | G1 |
| 1 | reset | G2 |
| 2 | prn[0] | Selected PRN |
| 3 | prn[1] | none |
| 4 | prn[2] | none |
| 5 | prn[3] | none |
| 6 | prn[4] | none |
| 7 | none | none |