pwmdac.abl

16V8例程,应用GEL16V8实现的振荡器,振荡频率为300k-20Hz

MODULE pwmdac

TITLE 'Pulse width modulated Digital to Analog converter'

@CARRY 2; 

"Constants
	c,x = .c.,.x.;

"Inputs
	clk,rclk,clr,d7..d0  pin;

"Outputs
	pwm                  pin istype 'com';
	load	             pin istype 'com';

"Nodes
	r7..r0               node istype 'reg,buffer';

"Sub-module declarations
	counter interface (clk,rst -> q7..q0);

"Sub-module instances
	cntr1 functional_block counter;

"Sets
    count = cntr1.[q7..q0];
    store = [r7..r0];


Equations

    pwm = (count > store);     " Pulse Width Modulated
                               " output is low until
                               " count goes beyond data.

    cntr1.clk = clk;           "
    cntr1.rst = clr;           " Clear counter on clr

    load = (count == 250);     " Time for next data byte.
                               " Externally connect load
                               " output to rclk input.
    store.clk = rclk;          " Load data when count
    store := [d7..d0];         " reaches appropriate point.

declarations

    testPWM macro (i) {
test_vectors   ([clk,clr,rclk,[d7..d0]] -> [pwm,load])
                [ 0 , 1 , .c.,   ?i   ] -> [ 0 ,  0 ];         
@repeat ?i     {[.c., 0 ,  0 ,    0   ] -> [ 0 ,  0 ];}
@repeat 248-?i {[.c., 0 ,  0 ,    0   ] -> [ 1 ,  0 ];}
                [.c., 0 ,  0 ,    0   ] -> [ 1 ,  0 ];
                [.c., 0 ,  1 ,    0   ] -> [ 1 ,  1 ];
                [.c., 1 ,  0 ,    0   ] -> [ 0 ,  0 ];
    }
testPWM(12);
testPWM(151);
testPWM(81);
testPWM(9);

END