Basic Characteristics RAPID

6.2 System signals
An output can be set to one or zero from within the program. This can also be done using
a delay or in the form of a pulse. If a pulse or a delayed change is ordered for an output,
program execution continues. The change is then carried out without affecting the rest
of the program execution. If, on the other hand, a new change is ordered for the same
output before the given time elapses, the first change is not carried out (see Figure 39).
1
Figure 39 The instruction SetDO is not carried out at all because a new command is given before
the time delay has elapsed.
Logical signals can be interconnected by means of special system functions. If, for
example, an input is connected to the system function Start, a program start is
automatically generated as soon as this input is enabled. These system functions are
generally only enabled in automatic mode. For more information, see Chapter 9,
System Parameters, or the chapter on Installation and Commissioning - PLC
Communication in the Product Manual.
6.3 Cross connections
SetDO \SDelay:=1, do1;
WaitTime 0.5;
PulseDO do1;
Signal value
0 0.5 1
Time
Digital signals can be interconnected in such a way that they automatically affect one
another:
- An output signal can be connected to one or more input or output signals.
- An input signal can be connected to one or more input or output signals.
- If the same signal is used in several cross connections, the value of that signal
is the same as the value that was last enabled (changed).
- Cross connections can be interlinked, in other words, one cross connection can
affect another. They must not, however, be connected in such a way so as to
form a ”vicious circle”, e.g. cross-connecting di1 to di2 whilst di2 is crossconnected
to di1.
- If there is a cross connection on an input signal, the corresponding physical
connection is automatically disabled. Any changes to that physical channel will
thus not be detected.
RAPID Reference Manual 6-39