Appendix A • Glossary
Appendix A
555Automation PC 620 with 945GME N270 CPU board User's Manual V 1.10
CTS
An abbreviation for "Clear To Send". 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 "Data Carrier Detected". 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
Direct Memory Access > Accelerated direct access to a computer’s RAM by bypassing the CPU.
DRAM
An abbreviation for "Dynamic Random Access Memory". Dynamic RAM consists of an
integrated semiconductor circuit that stores information based on the capacitor principle.
Capacitors lose their charge in a relatively short time. Therefore, dynamic RAM circuit boards
must contain a logic that allows continual recharging of RAM chips. Since the processor cannot
access dynamic RAM while it is being recharged, one or more waiting states can occur when
reading or writing data. Although it is slower, dynamic RAM is used more often than static RAM
since the simple design of the circuits means that it can store four times more data than static
RAM.
DSR
An abbreviation for "Data Set Ready". A signal used in serial data transfer, which is sent by the
modem to the computer it is connected to, indicating its readiness for processing. DSR is a
hardware signal which is sent via line number 6 in compliance with the RS-232-C standard.
DTR
An abbreviation for "Data Terminal Ready". A signal used in serial data transfer that is sent by
the computer to the modem it is connected to, indicating the computer's readiness to accept
incoming signals.
D
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