Glossary
141
unit address A number used to control network communications. Unit addresses are com-
puted for Units in various ways, e.g., 10 hex is added to the unit number to deter-
mine the unit address for a CPU Bus Unit.
unit number A number assigned to some Link Units, Special I/O Units, and CPU Bus Units to
facilitate identification when assigning words or other operating parameters.
uploading The process of transferring a program or data from a lower-level or slave com-
puter to a higher-level or host computer. If a Programming Device is involved,
the Programming Device is considered the host computer.
watchdog timer A timer within the system that ensures that the scan time stays within specified
limits. When limits are reached, either warnings are given or PC operation is
stopped depending on the particular limit that is reached.
WDT See watchdog timer.
wire communications A communications method in which signals are sent over wire cable. Although
noise resistance and transmission distance can sometimes be a problem with
wire communications, they are still the cheapest and the most common, and per-
fectly adequate for many applications.
word A unit of data storage in memory that consists of 16 bits. All data areas consists
of words. Some data areas can be accessed only by words; others, by either
words or bits.
word address The location in memory where a word of data is stored. A word address must
specify (sometimes by default) the data area and the number of the word that is
being addressed.
word allocation The process of assigning I/O words and bits in memory to I/O Units and termi-
nals in a PC System to create an I/O Table.
work area A part of memory containing work words/bits.
work bit A bit in a work word.
work word A word that can be used for data calculation or other manipulation in program-
ming, i.e., a ‘work space’ in memory. A large portion of the IR area is always re-
served for work words. Parts of other areas not required for special purposes
may also be used as work words.
write protect switch A switch used to write-protect the contents of a storage device, e.g., a floppy
disk. If the hole on the upper left of a floppy disk is open, the information on this
floppy disk cannot be altered.
write-protect A state in which the contents of a storage device can be read but cannot be al-
tered.
To Next Page
Loading...
Need help?
General
