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

196 Chapter9
Describing Asynchronous Devices
How to Control Terminals
Block Mode
When a terminal operates in block mode, characters are held in the
terminal's memory (buffer) as they are typed. Characters are not
transmitted to the DTC until a specific action is taken. Pressing
[Enter]
at the end of a block of data will normally send it to the DTC.
An application program can use an alternate method to end a block
mode read. Refer to “Terminating Reads” later in this chapter for more
information on ways to end a block mode read.
Block mode is enabled programmatically by executing a block mode
application at the terminal. The program needs to change the
terminal’s configuration settings. It should do this automatically by
sending escape sequences to the terminal.
Blocks of characters can be input to the DTC a line at a time (called line
block mode) or a page at a time (called page block mode), depending on
the type of block mode used. Because characters are displayed on the
screen as they are entered, local editing and cursor control features can
be used to alter a line or page before it is transmitted to the DTC.
Data is transmitted one character (literally one byte) at a time, with
each character bound by start bits and stop bits. Block mode sends data
in one transmission “burst,” although the characters are transmitted
one by one in a long stream.
Data Editing Modes
Data input from a terminal is usually intended as data for the
computer: commands, input to a program, etc. Some characters are not
interpreted as data, but as special characters. When these characters
are encountered, the DTC or the ASC software is signaled to perform a
specific function. The functions vary from deleting a character to
interrupting a program or subsystem.
The data editing mode defines which characters are recognized as
special characters by the system. The types of data editing modes are as
follows:
• Standard editing.
• Transparent editing.
• Binary editing.
Special character sets are defined for each editing mode. All special
characters apply in standard editing mode, fewer apply in transparent
editing mode, and no special characters are recognized in binary editing
mode. Refer to the Asynchronous Serial Communications Programmer’s
Reference Manual for more information on data editing modes.