LSIS XBE-DC08A, Руководство пользователя, Страница: 25 / 1284

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Chapter 1 Introduction
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(4) Protocol
This is communication rule established in relation between the transmission side and the receiving side of information in
order to send and accept information between two computers/terminals or more without error, effectively, and reliably. In
general, this specifies call establishment, connection, structure of message exchange form, re-transmission of error
message, procedure of line inversion, and character synchronization between terminals, etc.
(5) BPS(Bits Per Second)
와
CPS(Characters Per Second)
BPS is a unit of transfer rate that represents how many bits are transferred per second. CPS is the number of the
characters transferred for a second. Generally, one character is 1Byte (8Bits), so CPS is the number of bytes which can
be transferred per second.
(6) Node
Node is a term that means the connected nodes of the data in the network tree structure, generally network is composed
of a great number of nodes, and is also expressed as the station number.
(7) Packet
Packet, a compound term of package and bucket used for packet exchange type to send information as divided in a unit
of packet, separates transferred data into the defined length to add a header that presents the correspondent addresses
(station No., etc.) thereto.
(8) Port
Port is meant to be the part of the data process device which sends or receives the data from a remote control terminal in
data communications, but in Cnet serial communication is meant to be the RS-232C or RS-422 port.
(9) RS-232C
RS-232C is the interface to link a modem with a terminal and to link a modem with a computer, and is also the serial
communications specification established by EIA according to the recommendations of the CCITT. This is also used to
link the null modem directly as well as the modem linkage. The disadvantage is that the transfer length is short and that
only 1 : 1 communication is available, and the specifications which have overcome this disadvantage are RS-422 and
RS-485.
(10) RS-422/RS-485
As one of the serial transmission specifications, its transferring length is long with 1 : N connection available compared to
RS-232C. The difference of these two specifications is that RS-422 uses 4 signals of TX(+), TX(-), RX(+) and RX(-),
while RS-485 has 2 signals of (+) & (-), where data is sent and received through the same signal line. Accordingly, RS-
422 executes the full-duplex type of communication and RS-485 executes the half-duplex type of communication.