The communications character set is the character set used by EDT to exchange data with a terminal.
In Unicode mode, the communications character set can be different from the character set used in the current work file. Inputs and outputs are then converted accordingly if required.
Since VTSU is the interface to the terminal, the communications character set in interactive mode can only be a character set that is accepted by VTSU with the exception of
EDF03DRV at a 7-bit terminal (see section “The character set EDF03DRV”). Restrictions consequently apply to the choice of the communications character set.
On start-up, EDT sets the character set from the terminal option CODED-CHARACTER-SET as the communications character set. The @CODENAME statement (format 2) can be used to set the communications character set explicitly. This setting remains valid until modified by a subsequent @CODENAME statement.
@CODENAME *AUTO, TERMINAL can be used to activate a mechanism by which EDT automatically attempts to select the most suitable character set. If it is communicating with a Unicode-compatible emulation, it specifies UTFE as the communications character set.
In the case of a terminal operating in 8-bit mode, i.e. if no communication via UTFE is possible, then the communications character set is implicitly defined by the character set of the work file displayed in the (top) work window.
If this character set changes, e.g. if EDT displays a different character set then the communications character set may also change. If the work file is empty and has the character set *NONE then, by default EDT takes the character set from the terminal
option CODED-CHARACTER-SET. If 7-BIT is specified here, it uses EDF03IRV, otherwise the character set specified here. If the work file displayed in the (top) work window has a character set which is compatible with the terminal then this character set is specified.
If this character set is an ISO character set which is compatible with a character set which is itself compatible with the terminal then this is specified. If this is not the case, EDF041 is used.
For communications with a terminal in 7-bit mode, the communications character set EDF03IRV is always used.
The same rules apply in L mode. This also applies when reading from SYSDTA (@EDIT ONLY), and SYSDTA is assigned to a terminal.