Technical data

Table Of Contents
Glossary
System Software for S7-300/400 System and Standard Functions- Volume 2/2
A5E00739858-01
Glossary-3
Closed-Loop Controller
A closed-loop controller is a device in which the error signal is continuously
calculated and an actuating signal generated with the aim of eliminating the error
signal quickly and without overshoot.
Communication, Bilateral
When using communication SFBs for data exchange, a distinction is made
between unilateral and bilateral communication. Communication is bilateral when
there is a SFB on the local and the remote module, for example, the
communication SFBs "USEND" and "URCV."
Communication SFBs for Configured Connections
Communication SFBs are system function blocks for data exchange and program
management.
Examples of data exchange: SEND, RECEIVE, GET.
Examples of program management: setting the CPU of a communication partner to
the STOP state, querying the STATUS of the CPU of a communication partner.
Communication SFCs for Non-Configured Connections
Communication SFCs are system functions for data exchange and for aborting
existing connections established by the communication SFCs.
Communication, Unilateral
When using communication SFBs for data exchange, a distinction is made
between unilateral and bilateral communication. Communication is unilateral when
there is a SFB only on the local module, for example, the SFB "GET."
Complete Restart
When a CPU starts up (for example, when the mode selector is moved from STOP
to RUN or when power is turned on), before cyclic program processing starts
(OB1), either the organization block OB101 (restart; only in the S7-400) or OB100
(complete restart) is processed first. In a complete restart the process-image input
table is read in and the STEP 7 user program processed starting with the first
statement in OB1.
Constant
"Constants" are token values for constant values in logic blocks. Constants are
used to improve the legibility of a program. For example, instead of entering a
value directly (for example, 10), the token value "Max_iteration_count" is entered in
a function block. The value of the constant (for example, 10) is then entered when
the block is called.