16 flip flops are connected in a chain, and the output of some is XORed together and fed back into the first flip flop. The outputs that are XORed together are chosen in such a way as to give the longest possible cycle (2^16-1). All bits being zero is a special case and is treated separately (all negative outputs of the flip flops are ANDed together to generate a 1 as feedback). On each clock pulse (pin 1) one new bit is generated. Setting load_en (pin 3) to HIGH allows the loading of a user defined value through the data_in pin (pin2). On each clock pulse one bit is read into the flip flop chain. When load_en (pin 3) is set to LOW the computed feedback bit is fed back into the flip flops. The outputs of the last 8 flip flops are connected to the output pins. For each clock pulse a random bit is generated and the other 7 are shifted.
Set the switch for pin 1 so that the push button generates the clock. Press on it and see the output change on the hex display. Using pin 2 and 3 a custom value can be loaded into the flip flops.
| # | Input | Output |
|---|---|---|
| 0 | clock | random bit 0 |
| 1 | data_in | random bit 1 |
| 2 | load_en | random bit 2 |
| 3 | none | random bit 3 |
| 4 | none | random bit 4 |
| 5 | none | random bit 5 |
| 6 | none | random bit 6 |
| 7 | none | random bit 7 |