Rockwell Automation 1772-LS_LSP,D17726.8.6 PROG/OPER MANUAL-MINI PLC-2/05 - Manual (Page 255)

Glossary
Appendix B
BĆ19
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Commonly refers to the reading/writing of programs and data tables from or
into processor memory. The commands to do these processes come from some
supervisory device.
Upper Nibble
The four most significant bits of a byte.
Variable
A factor which can be altered, measured, or controlled.
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.
Watchdog Timer
A timer that monitors logic circuits controlling the processor. If the watchdog
timer is not reset in its programmed time period, it will cause the processor
to fault.
Word
A grouping or a number of bits in a sequence that is treated as a unit.
Word Length
A number of bits in a word. In a processor, these are generally only data bits.
One processor word equals 16 data bits.
Word Storage
An unused data table word which may be used to store data without directly
controlling an output. 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
1) The process of loading information into memory. 2) Block Transfer; a
transfer of data from the processor data table to an intelligent I/O module.
ZCL Instructions
A user-programmed fence for ZCL zones.
ZCL Zones
Assigned program areas which may control the same outputs through separate
rungs, at different times. Each ZCL zone is bound and controlled by ZCL