module cntdown;
title '6-bit down counter'
cntdown device 'P22V10';

declarations

CLK  pin 1;
LD   pin 2;
I3,I4,I5,I6,I7,I8    pin 3,4,5,6,7,8;

IO19,IO18,IO17,IO16  pin 19,18,17,16 istype 'reg_d,buffer';
IO15,IO14            pin 15,14 istype 'reg_d,buffer';

H,L,C,X,Z,P = 1,0,.C.,.X.,.Z.,.P.;

CNT = [IO19,IO18,IO17,IO16,IO15,IO14]; 
INPUT = [I3,I4,I5,I6,I7,I8];
        
equations

CNT.D = (CNT.FB - 1) & !LD
      # INPUT & LD;

CNT.CK = CLK;
CNT.OE = ^h3F;

@RADIX 16;
@CONST COUNT=3F;

TEST_VECTORS (
[CLK,LD,INPUT] -> [CNT]);
[ 0, 0, 00   ] -> [00 ];
[ C, 0, 00   ] -> [3F ];

@REPEAT 3D {
@CONST COUNT = COUNT - 1;
[ C, 0, 00   ] -> [COUNT]; }

[ C, 0, 00   ] -> [01 ];
[ C, 0, 00   ] -> [00 ];
[ C, 0, 00   ] -> [3F ];
[ C, 1, 22   ] -> [22 ];
[ C, 0, 22   ] -> [21 ];
[ C, 0, 22   ] -> [20 ];




end