Rockwell Automation 1772-LV Mini-PLC - 2/15 Programmable Controller (Series B) Programming and Operations - Manual (Page 210)

Glossary
Appendix B
BĆ17
Unlatch Instruction
A PC instruction which causes an output to stay off, regardless of how briefly
the instruction is enabled. (It can only be turned on by a latch instruction in a
separate rung.)
Variable Data
Numerical information which can be changed during application operation. It
includes timer and counter accumulated values, thumbwheel settings, and
arithmetic results.
Volatile Memory
A memory that loses its information if the power is removed from it and if it
does not have a backup power source.
Voltage
The term most often used in place of electromotive force, potential, potential
difference, or voltage drop. It describes the electric pressure that exists between
two points and is capable of producing a flow or current when a closed circuit is
connected between the two points.
Word
A grouping or a number of bits in a sequence that is treated as a unit.
Word Length
The number of bits in a word, in PC literature these are generally only data bits.
One PC word - 16 data bits.
Word Storage
An unused data table word which may be used to contain numerical information
without directly controlling any outputs. Any storage word may be monitored
as often as necessary by the user program.
Work Area
A portion of the data table reserved for specific processor functions.
Write
The process of leading information into memory.
ZCL Instructions
User-programmed fence for ZCL zones.
ZCL Zones
Distinct program areas which control the same outputs, through separate rungs,
at different times. Each ZCL zone is delimited and controlled by ZCL fences
(ZCL instructions). for any grouping of outputs, the user’s program must enable
only one ZCL zone at any time. (If all ZCL zones are disabled, the outputs
would remain in their last states.)