Sequential Logic

Each LUT pair can be connected to internal sequential logic: D flip flop, JK flip flop, gated D-latch or RS-latch can be selected by writing the corresponding Sequential Selection bits in Sequential Control x register (SEQCTRLx.SEQSEL). Before using sequential logic, the GCLK clock and optionally each LUT filter or edge detector, must be enabled.

Gated D Flip-Flop (DFF)

When the DFF is selected, the D-input is driven by the even LUT output (LUT2x), and the G-input is driven by the odd LUT output (LUT2x+1), as shown in Figure 1.

Figure 1. D Flip Flop

When the even LUT is disabled (LUTCTRL2x.ENABLE=0), the flip-flop is asynchronously cleared. The reset command (R) is kept enabled for one APB clock cycle. In all other cases, the flip-flop output (OUT) is refreshed on rising edge of the GCLK_CCL, as shown in Table 1.

Table 1. DFF Characteristics
R	G	D	OUT
1	X	X	Clear
0	1	1	Set
	1	0	Clear
	0	X	Hold state (no change)

JK Flip-Flop (JK)

When this configuration is selected, the J-input is driven by the even LUT output (LUT2x), and the K-input is driven by the odd LUT output (LUT2x+1), as shown in Figure 2.

Figure 2. JK Flip Flop

When the even LUT is disabled (LUTCTRL2x.ENABLE=0), the flip-flop is asynchronously cleared. The reset command (R) is kept enabled for one APB clock cycle. In all other cases, the flip-flop output (OUT) is refreshed on rising edge of the GCLK_CCL, as shown in Table 2.

Table 2. JK Characteristics
R	J	K	OUT
1	X	X	Clear
0	0	0	Hold state (no change)
0	0	1	Clear
0	1	0	Set
0	1	1	Toggle

Gated D-Latch (DLATCH)

When the DLATCH is selected, the D-input is driven by the even LUT output (LUT2x), and the G-input is driven by the odd LUT output (LUT2x+1), as shown in Figure 1.

Figure 3. D-Latch

When the even LUT is disabled (LUTCTRL2x.ENABLE=0), the latch output will be cleared. The G-input is forced enabled for one more APB clock cycle, and the D-input to zero. In all other cases, the latch output (OUT) is refreshed as shown in Table 3.

Table 3. D-Latch Characteristics
G	D	OUT
0	X	Hold state (no change)
1	0	Clear
1	1	Set

RS Latch (RS)

When this configuration is selected, the S-input is driven by the even LUT output (LUT2x), and the R-input is driven by the odd LUT output (LUT2x+1), as shown in Figure 4.

Figure 4. RS-Latch

When the even LUT is disabled (LUTCTRL2x.ENABLE=0), the latch output will be cleared. The R-input is forced enabled for one more APB clock cycle and S-input to zero. In all other cases, the latch output (OUT) is refreshed as shown in Table 4.

Table 4. RS-latch Characteristics
S	R	OUT
0	0	Hold state (no change)
0	1	Clear
1	0	Set
1	1	Forbidden state