Configuring Systems for Terminals, Printers, and Other Serial Devices (32022-90051)

190 Chapter9
Describing Asynchronous Devices
How to Control Terminals
How to Control Terminals
DTS helps control the operation of terminals. It automatically handles
the input and output of data to the terminal as explained earlier in this
chapter under “How to Control the Flow of Data.” Alternative methods
for controlling terminals are as follows:
• Echoing characters to the terminal screen as they are typed at the
keyboard.
• Allowing special characters to be processed as intended. For
example,
[Enter] signals the end of input data and the backspace
character causes an unwanted character to be deleted from input
data. Other examples of special characters include system break
(
[Break]) and subsystem break (usually [CTRL]-Y).
• Modifying the transmission speed through the SPEED or SET
commands.
It is possible to programmatically change the method that the DTS uses
to control a terminal. A program can change the following attributes:
• Parity error checking.
• The method of input for a read from character mode to block mode.
• The set of special characters recognized by the DTC.
• The maximum byte count or a maximum time to enter data.
Each of the methods for controlling terminals is explained in the
following pages. Refer to the Asynchronous Serial Communications
Programmer’s Reference Manual for more information on programmatic
device control.
Echo
When characters are typed on a keyboard, the terminal user expects
each character to appear on the screen as it is typed. This is referred to
as echo. Any of the following settings determine whether echo occurs:
• Local echo enabled.
• The modem echo is enabled.
• DTC echo is enabled.
• Typeahead echo is enabled.
Only one of these settings should be enabled at any time. Each of these
settings are described below. Hewlett-Packard recommends setting
DTC echo. (DTC echo is automatically enabled for devices configured as
terminals.)