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Glossary
FA Factory automation.
factory computer A general-purpose computer, usually quite similar to a business computer, that
is used in automated factory control.
FAL error An error generated from the user program by execution of an FAL(06) instruc-
tion.
FALS error An error generated from the user program by execution of an FALS(07) in-
struction or an error generated by the system.
fatal error An error that stops PC operation and requires correction before operation can
continue.
FCS See frame checksum.
flag A dedicated bit in memory that is set by the system to indicate some type of
operating status. Some flags, such as the carry flag, can also be set by the op-
erator or via the program.
flicker bit A bit that is programmed to turn ON and OFF at a specific frequency.
floating-point decimal A decimal number expressed as a number (the mantissa) multiplied by a pow-
er of 10, e.g., 0.538 x 10
–5
.
force reset The process of forcibly turning OFF a bit via a programming device. Bits are
usually turned OFF as a result of program execution.
force set The process of forcibly turning ON a bit via a programming device. Bits are
usually turned ON as a result of program execution.
forced status The status of bits that have been force reset or force set.
frame checksum The results of exclusive ORing all data within a specified calculation range.
The frame checksum can be calculated on both the sending and receiving end
of a data transfer to confirm that data was transmitted correctly.
function code A two-digit number used to input an instruction into the PC.
hardware error An error originating in the hardware structure (electronic components) of the
PC, as opposed to a software error, which originates in software (i.e., pro-
grams).
header code A code in an instruction that specifies what the instruction is to do.
hexadecimal A number system where all numbers are expressed to the base 16. In a PC all
data is ultimately stored in binary form, however, displays and inputs on Pro-
gramming Devices are often expressed in hexadecimal to simplify operation.
Each group of four binary bits is numerically equivalent to one hexadecimal
digit.
host computer A computer that is used to transfer data to or receive data from a PC in a Host
Link system. The host computer is used for data management and overall sys-
tem control. Host computers are generally small personal or business comput-
ers.
host interface An interface that allows communications with a host computer.
host link An interface connecting a PC to a host computer to enable monitoring or pro-
gram control from the host computer.
HR area A memory area that preserves bit status during power interrupts and used as
work bits in programming.
I/O bit A bit in memory used to hold I/O status. Input bits reflect the status of input ter-
minals; output bits hold the status for output terminals.
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