Configuring Systems for Terminals, Printers, and Other Serial Devices (32022-90057)

Describing Asynchronous Devices
How to Control Terminals
Chapter 9
179
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.
Terminating Reads
Reads can be programmatically terminated in one of several ways:
• An EOR or AEOR character is sent from the terminal.
• The input byte count is reached.
• The read limit timer expires.
• The block mode read timer expires.
• The system break character (if it is enabled) is sent from the terminal.
• The subsystem break character is sent from the terminal.
•The
[CTRL]-A
character is sent from the system console.
• The DTC encounters a parity error (only when parity checking is enabled).
Note that when using binary editing mode, a read cannot be terminated by any character.
Binary reads can be terminated only if either:
• The input byte count is reached.
• The read limit timer expires.