Siemens S7-300 Installation Manual page 217

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The Æ CPU uses the accumulator registers as intermediate memory for load,
transfer, comparison, calculation and conversion operations.
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An address represents the ID for a specific address or address range. Example:
Input I12.1; Memory bit word MW25; Data block DB3.
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Analog modules convert process values (e.g. temperature) into digital values, so
that they can be processed by the central processing unit, or convert digital values
into analog manipulated variables.
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The backplane bus is a serial data bus. It supplies power to the modules and is
also used by the modules to communicate with each other. Bus connectors
interconnect the modules.
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The back-up memory provides a back-up of memory areas for the Æ CPU without
a back-up battery. It backs up a configurable number of timers, counters, memory
bits, data bytes and retentive timers, counters, memory bits and data bytes).
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A bus is a communication medium connecting several nodes. Data can be
transferred via serial or parallel circuits, that is, via electrical conductors or fiber
optic.
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A bus segment is a self-contained section of a serial bus system. Bus segments
are interconnected using repeaters.
S7-300 Automation System, Hardware and Installation: CPU 312IFM - 318-2 DP
A5E00203919-01

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