FTC

Toggle Flip-Flop with Toggle Enable and Asynchronous Clear

FTC is a synchronous, resettable toggle flip-flop. The asynchronous clear (CLR) input, when High, overrides all other inputs and resets the data output (Q) Low. The Q output toggles, or changes state, when the toggle enable (T) input is High and CLR is Low during the Low-to-High clock 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, STARTUP_SPARTAN2, or STARTUP_VIRTEX symbol.

Inputs			Outputs
CLR	T	C	Q
1	X	X	0
0	0	X	No Chg
0	1		Toggle

Figure 5.49 FTC Implementation XC3000, XC4000E, XC4000X, XC5200, Spartan, SpartanXL, Spartan2, Virtex

Figure 5.50 FTC Implementation XC9000