Designing The Lf Control Byte With Venn Diagrams - Commodore Amiga Hardware Reference Manual

Equation-to-Minterm Conversion
An example of converting an equation to minterm format in order to derive the select
code is given below:
D
=
AB
+
AC (Starting equation)
D
=
AB (C
+
C)
+
AC (B
+
B)
(Multiplying by 1)
D
=
ABC
+
ABC
+
ABC
+
ABC (Final minterms)
This final form contains only terms that contain all of the input sources. These are the
min terms you use. These min terms are selected with the minterm enable bits LF7-LFO
as shown below:
ABC ABC
ABC ABC
ABC ABC ABC ABC
(Available
minterms)
(BLTCONO
1
1 0 0
1 0 1
0 LF 7-0 code in binary
C
A
LF 7-0 code in hex
DESIGNING THE LF CONTROL BYTE WITH VENN DIAGRAMS
You can use Venn diagrams as an aid in selecting minterms. The Venn diagram in
figure 6-3 shows a set of three circles labeled A, Band C. In the diagram, the numbers 0
through 7 in various areas correspond to the min term numbers shown in the preceding
section.
To select which min terms are necessary to produce a certain kind of equation result, you
need only examine the circles and their intersections and copy down the numbers seen
there.
Blitter Hardware 175