VHDL Programming

148 Chapter Six

CONSTANT andsd : t_4valX2 :=

((’x’, -- xx

’ 0 ’, -- x0

’x’, -- x1 (Notice this is an

’x’), -- xz array of arrays.)

(’ 0 ’, -- 0x

’ 0 ’, -- 00

’ 0 ’, -- 01

’ 0 ’), -- 0z

(’x’, -- 1x

’ 0 ’, -- 10

’ 1 ’, -- 11

’x’), -- 1z

(’x’, -- zx

’ 0 ’, -- z0

’x’, -- z1

’x’)); -- zz

CONSTANT andmd : t_4valmd :=

((’x’, -- xx

’ 0 ’, -- x0

’x’, -- x1

’x’), -- xz (Notice this example

(’ 0 ’, -- 0x is a multidimensional

’ 0 ’, -- 00 array.)

’ 0 ’, -- 01

’ 0 ’), -- 0z

(’x’, -- 1x

’ 0 ’, -- 10

’ 1 ’, -- 11

’x’), -- 1z

(’x’, -- zx

’ 0 ’, -- z0

’x’, -- z1

’x’)); -- zz

END p_4val;

The two composite type constants,andsdand andmd, provide a lookup

table for an ANDfunction of type t_4val. The first constant andsduses an

array of array values, while the second constant andmduses a multi-

dimensional array to store the values. The initialization of both constants

is specified by the same syntax. If the ’LENGTHattribute is applied to these

types as shown in the following, the results shown in the VHDL comments

are obtained:

PROCESS(a)

VARIABLE len1, len2, len3, len4 : INTEGER;

BEGIN

len1 := t_4valX1’LENGTH; -- returns 4

len2 := t_4valX2’LENGTH; -- returns 4