ABSTRACT
We begin the discussion of RTDB objects with digital input (DI) and output (DO). Both objects are similar considering their values. In Boolean algebra they are treated as two values (
false
,
true
) signals. In the Vfsm concept, DI have three control values:
LOW
,
HIGH,
and
UNKNOWN
and there are two actions defined for DO:
Low
and
High
. Figure 11.1 shows the state transition diagram of a DI object controlled
by the external I/O signals
Di_LOW
,
Di_HIGH
,
Di_UNKNOWN
. We chose
LOW
and
HIGH
deliberately, although they are clearly not appropriate in all situations. They correspond to an electronic engineer’s view of such signals, of course. One could argue for the more general names
and
, or
TRUE
and
FALSE
, for example, but we wish to highlight the distinction between these values and binary Boolean values.
