152 Chapter Six
A typical use of a function type attribute is to convert from an enu-
merated or physical type to an integer type. Following is an example of
conversion from a physical type to an integer type:PACKAGE ohms_law IS
TYPE current IS RANGE 0 TO 1000000
UNITS
ua; -- micro amps
ma = 1000 ua; -- milli amps
a = 1000 ma; -- amps
END UNITS;TYPE voltage IS RANGE 0 TO 1000000
UNITS
uv; -- micro volts
mv = 1000 uv; -- milli volts
v = 1000 mv; -- volts
END UNITS;TYPE resistance IS RANGE 0 TO 100000000
UNITS
ohm; -- ohms
Kohm = 1000 ohm; -- kilo ohms
Mohm = 1000 Kohm;-- mega ohms
END UNITS;
END ohms_law;use work.ohms_law.all;
ENTITY calc_resistance IS
PORT( i : IN current; e : IN voltage;
r : OUT resistance);
END calc_resistance;ARCHITECTURE behave OF calc_resistance IS
BEGIN
ohm_proc: PROCESS( i, e )
VARIABLE convi, conve, int_r : integer;
BEGIN
convi := current’POS(i); -- current in ua
conve := voltage’POS(e); -- voltage in uv-- resistance in ohms
int_r := conve / convi;r <= resistance’VAL(int_r);-- another way to write this example
-- is shown below
-- r <=resistance’VAL(current’POS(i)
-- / voltage’POS(e));