Asynchronous Serial Communications Programmer's Reference Manual (32022-90052)

Chapter 1 23
Introduction
Asynchronous Serial Communications
Terminals
A terminal is a hardware device that enables an end user to
communicate with the computer, and both send data to and receive data
from the system. All terminals supported for use on MPE/iX systems
include typewriter-like keyboards and CRT screens. Some personal
computers capable of running in terminal emulation mode are also
supported for asynchronous connection.
Terminal types are assigned to each terminal port configured for the
system and serve to help define the terminal’s features. For a complete
discussion of terminal types see Configuring Systems for Terminals,
Printers, and Other Serial Devices.
Serial Printers
Like terminals, serial printers can be connected to the system using
asynchronous serial communications. Unlike terminals, serial printers
are used only to receive information and to transfer that information to
paper in a permanent, readable format. Printer types are used to help
define the characteristics of each serial printer port configured for the
system. A complete discussion of printer types can be found in the
Configuring Systems for Terminals, Printers, and Other Serial Devices
manual.
Plotters
Plotters are special graphic devices which allow you to transfer
computer generated drawings to paper by plotting their X and Y
coordinates and moving pens to corresponding locations on the output
surface of the plotter.
Modems
In some cases asynchronous communications may take place over
telecommunication lines. Because the signal used by computers (digital
signal) is different from the signal transmitted over telephone lines
(analog signal), a device called a modem is required on each end of
such a link. The word “modem” comes from “modulator/demodulator”,
which describes the function of the device.
System Console
The system console is a terminal used by the system operator to
execute specific tasks for the purpose of managing sessions, jobs, and
system resources. A system console is connected to each HP 3000 Series
900 computer through a special access port, and system console
functions are controlled through the Console Management software.
Some of the console functionality can be temporarily transferred to
another terminal, or logical console. This can be useful if it is
necessary to receive console messages on another device. Most system
control functions, however, cannot be executed from a logical console.