Rockwell Automation 1747-DCM,D17476.8 Direct Communication Module - Manual (Page 12)

Preface
P–4
The following terms and abbreviations are specific to this product. For a
complete listing of Allen–Bradley terminology, refer to the Allen–Bradley
Industrial Automation Glossary, Publication Number ICCG–7.1.
Adapter – Any physical device that is a slave on the RIO link.
Adapter Image – The portion of scanner image assigned to an individual
adapter. You configure the adapter image by assigning it a starting logical
rack number, starting logical group number and the number of logical groups
it uses. In the case of the DCM, this is referred to as the DCM image.
DCM – Refers to the Direct Communication Module.
Distributed Control/Controller – Refers to a control system that employs a
number of different hardware controllers/processors, each designed to
perform a different subtask on behalf of an overall program or process. In a
single processor (non–distributed) system, each task would be done by the
single processor controlling the process. In a distributed system, each task is
targeted to the specific processor required to perform its needs. Since all
processors run simultaneously and independently, the time required to
perform each task of the overall process is reduced in comparison to a single
processor system. Therefore, overall program or process performance is
typically better.
Inhibit – A function by which the scanner stops communicating with a
logical device. The logical device will consider itself inhibited if it does not
receive communications from the scanner within a certain period of time.
Logical Device – Any portion of a logical rack assigned to a single adapter.
Logical Group – A logical group consists of one input and one output word
within a logical rack. A word consists of 16 bits, each bit represents one
terminal on a discrete I/O module. Also referred to as an I/O Group.
Logical Rack – A fixed section of the scanner image comprised of eight
input words and eight output words. Also referred to as a rack.
Logical Slot – A logical slot consists of one input and one output byte within
a logical group. A byte consists of 8 bits, each bit represents one terminal on
a discrete I/O module.
Physical Device – The number of devices that the supervisory processor/
scanner will support.
PLC Chassis – A physical PLC (Programmable Logic Controller) rack that
houses PLC processors and 1771 I/O modules.
Terms and Abbreviations