FJKP

J-K Flip-Flop with Asynchronous Preset

FJKP is a single J-K-type flip-flop with J, K, and asynchronous preset (PRE) inputs and data output (Q). The asynchronous preset (PRE) input, when High, overrides all other inputs and sets the Q output High. When PRE is Low, the Q output responds to the state of the J and K inputs, as shown in the following truth table, during the Low-to-High clock transition.

For FPGAs, the flip-flop is asynchronously preset, output High, when power is applied. FPGAs simulate power-on when global reset (GR for XC5200) or global set/reset (GSR for XC4000, Spartans, Virtex) is active. The GR/GSR active level defaults to active-High but can be inverted by adding an inverter in front of the GR/GSR input of the STARTUP, STARTUP_SPARTAN2, or the STARTUP_VIRTEX symbol.

For CPLDs, the flip-flop is asynchronously cleared, output Low, when power is applied. The power-on condition can be simulated by applying a High-level pulse on the PRLD global net.

Inputs				Outputs
PRE	J	K	C	Q
1	X	X	X	1
0	0	0	X	No Chg
0	0	1		0
0	1	0		1
0	1	1		Toggle

Figure 5.40 FJKP Implementation XC4000E, XC4000X, XC5200, Spartan, SpartanXL, Spartan2, Virtex

Figure 5.41 FJKP Implementation XC9000