Hardware Reference
In-Depth Information
Figure 11.7
Setting a reference value (for any set size). (a, b) Up only. (c, d) Up and down.
Figure 11.8
Practical application for a reference-value dei ner with a large number of states and timed
transitions.
The second case, presented in i gures 11.7c,d, has up and down controls. Again,
the output must range from
ref
min
to
ref
max
, with
up
and
dn
causing
ref
to be incremented
or decremented, respectively. When one of these limits is reached, the machine must
remain there until a movement (with
up
or
dn
) in the opposite direction is provoked.
A possible solution is depicted in i gure 11.7d. Again, the number of states is just four,
regardless of the number of reference values. Similarly to the previous case, here too
there are states (C and D) that must last only one clock period.
A practical application is presented in i gure 11.8a, where
up
is produced by a
pushbutton (after a debouncing circuit—see sections 8.11.3 and 11.7.4) and
ref
(refer-
ence value) is an eight-bit value, thus capable of operating anywhere in the 0-to-255
