dff_xbit :
A D flip-flop with xbit-type input/output’s.

The dff_xbit primitive models a D flip-flop with a data input d, a clock input clk, and an output q. All the input and output signals are xbit-typed. This primitive is suitable when processing digital signals with precise timing information.

The parameter trig_edge specifies whether the D flip-flop is triggered by the positive edge (+1), negative edge (-1), or both edges (0) of the clock clk. The parameter init_value defines the initial value of the output q.

The parameter delay_cq defines the propagation delay from the triggering edge of the clock to the output q. This delay is inertial, meaning that if a new triggering clock edge arrives before the previous change propagates to the output, the output change will be overriden with the one corresponding to the new triggering clock event.

When the parameter setup_time or hold_time is specified, the primitive also checks the setup or hold timing constraints, respectively. The parameter setup_time defines the amount of time the input d must be stable before the triggering edge of the clock and the parameter hold_time defines the amount of time the input d must be stable after the triggering edge of the clock. The parameter check_mode defines the action when a timing constraint is violated, whether the primitive changes its output q to a value x (1), displays a warning message (2), or does both (3).

Input/Output Terminals

Name	I/O	Type	Description
q	output	xbit	data output
d	input	xbit	data input
clk	input	xbit	clock input

Parameters

Name	Type	Default	Unit	Description
trig_edge	integer	1	None	triggering clock edge
init_value	logic	1’bx	None	initial value
delay_cq	real	0.0	seconds	clk-to-q delay
setup_time	real	`NaN	seconds	setup time constraint
hold_time	real	`NaN	seconds	hold time constraint
check_mode	integer	1	None	action for violation