Siemens SIMATIC S7-300 Series Reference Manual page 176

Glossary
FB
³ Function block
FC
³ Function
Flash EPROM
FEPROMs are the same as electrically erasable EEPROMS in that they can
retain data in the event of a power failure, but they can be erased much more
quickly (FEPROM = Flash Erasable Programmable Read Only Memory). They
are used on ³ Memory Cards.
Force
The "Force" function overwrites a variable (e.g. memory marker, output) with a
value defined by the S7 user. This variable is then write protected to prevent
modification by any other operation (including the STEP 7 user program). The
value is retained after the programming device is disconnected. The write
protection is not canceled until the "Unforce" function is called and the variable is
written again with the value defined by the user program. During commissioning,
for example, the "Force" function allows certain outputs to be set to the "ON"
state for any length of time even if the logic operations of the user program are
not fulfilled (e.g. because inputs are not wired).
Function
A function (FC) according to IEC 1131-3 is a ³ code block containing no ³
static data. A function allows parameters to be passed in the user program.
Functions are therefore suitable for programming complex functions, e.g.
calculations, which are repeated frequently.
Function block
A function block (FB) according to IEC 1131-3 is a ³ code block containing
³ static data. An FB allows parameters to be passed in the user program.
Function blocks are therefore suitable for programming complex functions, e.g.
closed-loop controls, mode selections, which are repeated frequently.
Glossary-6
PLC S7-300, CPU Specifications CPU 312 IFM to CPU 318-2 DP
A5E00111190-01