$2$ Given the following AHDL code,

$($a$)$ Explain the function of this code. Refer to parts of the code and

be specific in your answer.

$($b$)$ Explain the roles of $c[1$dots$0]$ and $tc.$

SUBDESIGN test$2$

$($

clock, c$[1.\mathrm{.}0]$ :INPUT;

q$[3.\mathrm{.}0],$ tc :OUTPUT;

VARIABLE

count $[3.\mathrm{.}0]$ :DFF;

BEGIN

DEFAULTS

$tC=VCC$;

END DEFAULTS;

count $[].$clk $=$ clock;

CASE $c[]$ IS

WHEN H$"$O$"=>$ count $[].d=0$;

WHEN H$"1"=>$

IF count $[]==0$ THEN

count$[].$d $=9$; tc $=$ GND;

ELSE count $[].$d $=$ count $[].$q $-1$;

END IF;

WHEN H$"2"=>$

IF count $[]==9$ THEN

count $[].$d $=0$ ; tc $=$ GND;

ELSE count $[].d=$ count $[].q+1$;

END IF;

WHEN H$"3"=>$ count $[].$d $=$ count $[].$q;

END CASE;

$q[]=$ count $[].$q;

END;