1.4.2 Communication model
Figure 2 illustrates the ways that values of variables can be communicated among software elements.
As shown in figure 2 a), variable values within a program can be communicated directly by connection
of the output of one program element to the input of another. This connection is shown explicitly in
graphical languages and implicitly in textual languages.
Variable values can be communicated between programs in the same configuration via global
variables such as the variable x illustrated in figure 2 b). These variables shall be declared as GLOBAL
in the configuration, and as EXTERNAL in the programs, as specified in 2.4.3.
As illustrated in figure 2 c), the values of variables can be communicated between different parts of a
program, between programs in the same or different configurations, or between a programmable
controller program and a non-programmable controller system, using the communication function
blocks defined in IEC 61131-5 and described in 2.5.2.3.5. In addition, programmable controllers or
non-programmable controller systems can transfer data which is made available by access paths, as
illustrated in figure 2 d), using the mechanisms defined in IEC 61131-5.
PROGRAM A
FB_X
a
FB1
FB_Y
b
FB2
Figure 2 a) - Data flow connection within a program
PROGRAM A
FB_X
a
FB1
PROGRAM B
FB_Y
b
FB2
x
x
VAR_GLOBAL
x: BOOL;
END_VAR
VAR_EXTERNAL
x: BOOL;
END_VAR
VAR_EXTERNAL
x: BOOL;
END_VAR
CONFIGURATION C
Figure 2 b) - Communication via GLOBAL variables
IEC 2469/02
IEC 2470/02
Copyright International Electrotechnical Commission
Provided by IHS under license with IEC
Not for Resale
No reproduction or networking permitted without license from IHS
--``````-`-`,,`,,`,`,,`---
61131-3
IEC:2003(E)
– 17 –
PROGRAM A
FB_X
FB1
CONFIGURATION C
SEND
send1
a
SD1
FB_Y
b
FB2
CONFIGURATION D
RCV
rcv1
RD1
PROGRAM B
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