Glossary
Appendix D
D-24
Upload/Download
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.
Wall Clock/Calendar
A device that continually measures time in a system without respect to
what tasks the system is performing.
Watchdog Timer
A timer that monitors logic circuits controlling the processor. If the
watchdog timer is not 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
The number of bits in a word. In a processor, these are generally only data
bits. One processor word = 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
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