478 terms ch 04
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a character, placed at the end
of a data block, that corresponds to the characteristics of block.
Block check character (BCC)
a transmission verification algorithm that adds
the binary values of all the characters in a data block and places the sum in
the block check character position.
a transformer that maintains
a steady output voltage (secondary) regardless of input voltage (primary)
Constant voltage transformer
an error detection method
in which the words in the data block are exclusive-ORed with the checksum word
and then rotated to the left.
Cyclic exclusive-OR checksum (CX-ORC)
an error detection method in
which all the bits in a block are divided by a predetermined binary number. The
remainder becomes the block check character.
Cyclic redundancy check (CRC)
the detection and isolation of an error or
an error-detecting code that combines parity
and data bits to generate a byte containing a value that identifies the
the process of revising the bits in a
PLC’s I/O tables based on the latest results from reading the inputs and processing
the outputs according to the control program.
I/O update scan
a transformer that protects its
connected devices from surrounding electromagnetic interference.
technique based on accumulated exclusive-OR of transmitted characters.
Longitudinal redundancy check (LRC)
a digital, electronic logic package capable
of performing the program execution, control, and data-processing functions of
a central processing unit. The contains an arithmetic logic unit, temporary
storage registers, instruction decoder circuitry, a program counter, and bus
a portable device used for programming,
changing, and monitoring a PLC’s control logic.
concurrent execution of two or more tasks
residing in memory.
the even or odd characteristic of the number of 1s
in a byte or word of memory.
a bit added to a memory word as a means of
the time required by the processor to
evaluate and execute the control logic.
the time required to complete the scan or two
activate and output that is controlled by programmed logic.
an error detecting method
in which a parity bit is added to each character in a message so that the
number of bits in each character is either at or even.
Vertical redundancy check (VRC)
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