| XC3000 | XC4000E | XC4000X | XC5200 | XC9000 | Spartan | SpartanXL | Virtex |
|---|---|---|---|---|---|---|---|
| Macro | Macro | Macro | Macro | Macro | Macro | Macro | Primitive |
FDS is a single D-type flip-flop with data (D) and synchronous set (S) inputs and data output (Q). The synchronous set input, when High, sets the Q output High on the Low-to-High clock (C) transition. The data on the D input is loaded into the flip-flop when S is Low during the Low-to-High clock (C) transition.
The flip-flop is asynchronously cleared, output Low, when power is applied. For CPLDs, the power-on condition can be simulated by applying a High-level pulse on the PRLD global net. FPGAs simulate power-on when global reset (GR) or global set/reset (GSR) is active. GR for XC3000 is active-Low. GR for XC5200 and GSR (XC4000, Spartans, Virtex) default to active-High but can be inverted by adding an inverter in front of the GR/GSR input of the STARTUP or STARTUP_VIRTEX symbol.
| Inputs | Outputs | ||
|---|---|---|---|
| S | D | C | Q |
| 1 | X |  | 1 |
| 0 | 1 | | 1 |
| 0 | 0 | | 0 |
Figure 5.27 FDS Implementation XC3000, XC4000, XC5200, XC9000, Spartans |  |
