address|[PLC] The location in memory where data is stored. For data areas, an address consists of
a two letter data area designation and a number that designate the word and/or bit
location. For the UM area, an address designates the instruction location (UM area); for the
FM area, the block location (FM area), etc.
allocation|[PLC] The process by which the PC assigns certain bits or words in memory for various
functions. This includes pairing I/O bits to I/O points on Units.
Analog Input Unit|[PLC] A Special I/O Unit that converts external analog input signals to digital input signals
for the PC. The analog signals can be voltages or amperages.
Analog I/O Unit|[PLC] A collective term for Analog Input Unit and Analog Output Unit.
Analog Output Unit|[PLC] A Special I/O Unit that converts digital output signals from the PC to analog output
signals for field devices. The analog signals can be voltages or amperages.
Analog Timer Unit|[PLC] A dedicated timer that interfaces through analog signal externally and digital signals
internally.
AND|[PLC] A logic operation whereby the result is true if and only if both premises are true. In
ladder diagram programming the premises are usually ON/OFF states of bits or the logical
combination of such states called execution conditions.
BCD|[PLC] Short for binary-coded decimal.
BCD calculation|[PLC] An arithmetic calculation that uses numbers expressed in binary-coded decimal.
binary|[PLC] A number system where all numbers are expressed to the base 2. Although in a
PC all data is ultimately stored in binary form, binary is used to refer to data that is
numerically equivalent to the binary value. It is not used to refer to binary coded decimal.
Each four binary bits is equivalent to one hexadecimal digit.
binary-coded decimal|[PLC] A system used to represent numbers so that each four binary bits is numerically
equivalent to one decimal digit.
bit|[PLC] The smallest unit of storage in a PC. The status of a bit is either ON or OFF. Four
bits equal one digit; sixteen bits, one word. Different bits are allocated to special purposes
, such as holding the status input from external devices, while other bits are available for
general use in programming.