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Appendix
D
Glossary
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This glossary contains definitions of terms commonly used in
Allen-Bradley scanner documentation.
ASIC
ASIC is an acronym for application-specific integrated circuit.
Block transfer
The transfer of data to or from an intelligent I/O module, as many as
64 words at a time.
Discrete I/O
I/O characterized by one terminal per image table bit (terminal and
point are the same).
End of interrupt (EOI)
Command issued to programmable interrupt controller to acknowledge
interrupts.
Fault dependent group
A group of I/O adapters treated as a single entity for the purposes of
fault detection. If one of the defined group faults all in the group are
in fault.
Half slot addressing
Addressing where an I/O group represents one half of a slot.
High density module
Discrete I/O module having 16 input or output points.
Input image table
An area of memory that monitors input terminals of input modules.
When an input switch is closed, its corresponding input bit is set.
Two hundred fifty-six 16-bit words (4096 points) are available.
Interrupt service routine (ISR)
A function that is vectored to when an interrupt occurs.
I/O chassis
One of four housings sized to hold 4, 8, 12, or 16 discrete I/O modules.
I/O group
An addressing concept representing 16 input bits (one input image
table word) and 16 output bits (one output image table word).
In hardware, an I/O group can represent one or two slots in an I/O
chassis. It has an address number.
I/O rack number
An addressing concept representing 8 I/O groups. An I/O rack number
can be distributed over one, two, three, or four I/O chassis; or two rack
numbers can be assigned to one I/O chassis, depending on chassis size
and your application requirements.
D-1
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