Jump instruction
Return instruction
Networks
Exception
RETURN
Exception:
Jump label
Instructions or user-defined function blocks
Input parameters
Output parameters
1
2
3
The networks shown above include a Jump instruction that changes the top-to-bottom flow of execu-
tion between networks, a label that shows the network to jump to, and a Return instruction.
Refer to Execution Order of Safety Programs Written in the FBD Language on page 6 - 22 and
Exe-
cution Control on page 6 - 23 later in this manual, and also to the NX-series Safety Control Unit
Instructions Reference Manual (Cat. No. Z931) for details.
Additional Information
• Unlike the ladder diagram language, the FBD language does not have bus bars. The con-
necting lines do not indicate power flow. They indicate the flow of data. The FBD language
does not have an END instruction. Execution for the task period ends when the last network
is executed.
•
In this manual, "FBD network" is sometimes used to differentiate programming networks from
physical networks, such as EtherCAT networks.
Execution Order of Safety Programs Written in the FBD Language
In POUs that are written in the FBD language, networks are executed in order from top to bottom.
Processing ends when the network at the very bottom of the program is executed.
Elements in the same network are executed from top to bottom for FUN and FB inputs and left to right
for blocks that are connected in series. In the following example, execution is in the following order:
Block 1, Block 2, Block 3, and then Block 4.
6 Programming
6 - 22
NX-series Safety Control Unit User's Manual (Z930)
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