Point-To-Point Or Multipoint - HP 262SA Reference Manual

Data Communications
Synchronous
Half Duplex
Full Duplex
A mode of transmission in which data is sent in a continuous stream with no
intervals between successive characters. When there is no data being sent
the communications line is in the cCidle" or cC ones " state. At the start of, and
during, each transmission the terminal and the computer maintain
synchronization with one another through the use of SYN (ASCII decimal
code 22) control characters.
A data link in which data can be transmitted in only one direction at a time.
Each time the direction of the data flow is reversed, the modems on each end
of the line must switch from CCtransmit"state to cCreceive"state (or vice versa).
This state transition is called a CCline turnaround".
A data link in which data can be transmitted in both directions simulta-
neously.
Character Mode When the terminal is operating in Character mode, it sends data characters
to the computer one at a time as they are typed into the keyboard.
Block Mode
When the terminal is operating in Block mode, data characters typed into the
keyboard are merely stored in display memory. When a block transfer is
subsequently triggered (by the host computer or by pressing the. key or
another appropriately defined key), a group of data characters is sent from
the terminal to the computer as a block.
POINT-TO-POINT OR MULTIPOINT
The first decision you must make is whether to establish a point-to-point or multipoint
configuration.
The term CCmultipoint" as used in this manual refers to a Hewlett-Packard multipoint terminal
configuration in which up to 32 terminals may share a single data link. This type of configura-
tion provides more extensive transmission error checking than is performed in point-to-point
and it provides an opportunity for noticeable cost savings through the use of shared resources
(modems, data lines, computer interface channels). Terminals within an HP multipoint config-
uration are physically organized into groups. Within each group the terminals are daisy-
chained to one another, with distances up to 2000 feet between terminals. Each daisy-chained
group shares a single modem or hardwired link to the host computer.
HP multipoint configurations operate only in Block mode and they may only be used in
conjunction with a host computer that supports this capability both from a hardware and
systems software standpoint.
A point-to-point configuration, on the other hand, is the standard form ofdata communications
within the industry (it is sometimes referred to as a cCTeletype-compatible" data link). Point-to-
point is supported by most computers. At any given time it accomodates only one terminal per
data link; it may, however, operate in either Character mode or Block mode.
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