39
Glossary
address 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 in-
struction location (UM area); for the FM area, the block location (FM area),
etc.
allocation 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.
AR area A PC data area allocated to flags, control bits, and word bits.
ASCII Short for American Standard Code for Information Interchange. ASCII is
used to code characters for output to printers and other external devices.
Backplane A base to which Units are mounted to form a Rack. Backplanes provide a
series of connectors for these Units along with wiring to connect them to the
CPU and Power Supply. Backplanes also provide connectors used to con-
nect them to other Backplanes. In some Systems, different Backplanes are
used for different Racks; in other Systems, Racks differ only by the Units
mounted to them.
back-up A copy of existing data which is valuable if data is accidentally erased.
BCD Short for binary-coded decimal.
BCD calculation An arithmetic calculation that uses numbers expressed in binary-coded deci-
mal.
binary-coded decimal A system used to represent numbers so that each four binary bits is numeri-
cally equivalent to one decimal digit.
bit The smallest piece of information that can be represented on a computer. A
bit has the value of either zero or one, corresponding to the electrical signals
ON and OFF. A bit is one binary digit.
bit address The location in memory where a bit of data is stored. A bit address must
specify (sometimes by default) the data area and word that is being ad-
dressed as well as the number of the bit.
bit number A number that indicates the location of a bit within a word. Bit 00 is the right-
most (least-significant) bit; bit 15 is the leftmost (most-significant) bit.
block instruction A special class of instruction used within ladder-diagram programming to al-
low flowchart-like coding, which is often difficult to write with ladder diagrams.
Function codes for block instructions are indicated between pointed paren-
theses<like this>.
block program A section of program written within a ladder diagram but based on block in-
structions. Block programs can also contain some, but not all, of the ladder-
diagram instructions.
To Next Page
Loading...
Need help?
General
