Glossary
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timer
A location in memory accessed through a TC bit and used to time down from
the timer’s set value. Timers are turned ON and reset according to their
execution conditions.
transfer
The process of moving data from one location to another within the PC, or
between the PC and external devices. When data is transferred, generally a
copy of the data is sent to the destination, i.e., the content of the source of
the transfer is not changed.
UM area
The memory area used to hold the active program, i.e., the program that is
being currently executed.
watchdog timer
A timer within the system that ensures that the scan time stays within speci-
fied limits. When limits are reached, either warnings are given or PC opera-
tion is stopped depending on the particular limit that is reached.
word
A unit of data storage in memory that consists of 16 bits. All data areas con-
sists 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.
work bit
A bit that can be used for data calculation or other manipulation in program-
ming, i.e., a ‘work space’ in memory.