Bernecker + Rainer 5PC820.SX01-00, User Manual, Page: 286 / 318

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Appendix A • Glossary
Automation PC 820 User's Manual V 1.20
CPU
An abbreviation for " C entral P rocessing U nit". Interprets and executes commands. It is also
known as a "microprocessor" or "processor" for short. A processor is able to receive, decode and
execute commands, as well as transfer information to and from other resources via the computer
bus.
CRT
Abbreviation for Cathode Ray Tube. The main component of a television set or a standard
computer screen. A cathode ray tube consists of a vacuum tube that contains one or more
electron guns. Each electron gun creates a horizontal electron beam that appears on the front
of the tube (the screen). The inner surface of the screen is coated with phosphor, which is lit
when hit by the electrons. Each of the electron beams move in a line from top to bottom. In order
to prevent flickering, the screen content is updated at least 25 times per second. The sharpness
of the picture is determined by the number of pixels on the screen.
CTS
An abbreviation for " C lear T o S end". A signal used when transferring serial data from modem to
computer, indicating its readiness to send the data. CTS is a hardware signal which is transferred
via line number 5 in compliance with the RS-232-C standard.
DCD
An abbreviation for " D ata C arrier D etected". A signal used in serial communication that is sent
by the modem to the computer it is connected to, indicating that it is ready for transfer.
Dial-up
Data is transferred over the telephone network using a modem or an ISDN adapter.
DIMM
"Double In-line Memory Module" consisting of one or more RAM chips on a small circuit board
that is connected with the motherboard of a computer.
DMA
D irect M emory A ccess > Accelerated direct access to a computer’s RAM by bypassing the CPU.
D