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

82 Chapter3
Common Device Control Functions
Altering Terminal Deficefiles
Setting Transparent Editing Mode
The FCONTROL intrinsic is also commonly used to set the data editing
mode at a terminal. As explained earlier in this chapter, the data
editing mode controls which characters are considered to have special
meaning when they are encountered in the data stream.
In standard editing mode, all special characters recognized by MPE/iX
apply and are acted on when sent from a terminal. However, there are a
number of reasons why you might want to suspend the special
processing associated with some of these characters. Your application
may be using one or more of these characters for a different purpose. Or
you may be using an unsupported device which transmits signals that
cause problems in standard editing mode.
One solution is to enable binary editing mode, which performs no
special character processing and allows all characters to pass through
as data. However, the use of binary mode severely limits the
transmission and terminal control options available to you.
Transparent editing mode provides a data editing level between
standard and binary editing modes. Because a limited number of
special characters retain their meaning in transparent mode, there is
much more flexibility in how a data transfer may take place than there
is when binary mode is used. For example, you can perform block mode
reads while in transparent editing mode, because the block mode
control characters (DC1 and DC2) retain their special meanings. (DC2
only has special meaning when received as the first byte of data,
however.) Transparent mode also allows you to use parity checking and
recognizes and responds to the AEOR character, if one has been
designated.
If transparent editing mode is enabled for any file, it is also in effect for
any other files opened on the same device, regardless of whether or not
it was specifically enabled for those files. Also, any FCLOSE issued
against the device will return the device to standard editing mode.
Subsystem break processing is also available in transparent editing
mode. The character that will be recognized as the subsystem break
character is passed in the intrinsic call. Any character not otherwise
recognized as a special character can be used, including the normal
subsystem break character,
[CTRL]Y. If a 0 is specified, subsystem break
will be disabled. You should note, however, that simply designating a
subsystem break character does not enable subsystem break
processing.
You must still enable subsystem break response and arm the
[CTRL]Y
trap before the subsystem break function can be invoked.
Transparent editing mode will be overridden if you should enable
binary editing mode at the same device. However, when you leave
binary mode, the device will still be operating in transparent mode. You