Dynamic modification of DBCS/EBCDIC mixed data

Programmed symbols and input control attribute bytes can be dynamically modified to permit EBCDIC or EGCS data to be mapped to a particular field on the 3270 display. DBCS/EBCDIC mixed data can also be dynamically modified. DBCS is a subset of EGCS, so the EGCS field can contain DBCS data, as shown in the following figure.

EBCDIC field and ECGS field are shown mapping into a larger mixed field of DBCS/EBCDIC.

The IMS application program can make a field EBCDIC, EGCS, or DBCS/EBCDIC mixed when all of the following conditions are satisfied:

One of the following is specified on the DFLD statement:
```
           EATTR=(EGCS,MIXD)
           EATTR=(EGCS'00',MIX)
           EATTR=(EGCS'00',MIXD)
```
A DBCS keyword does not exist; DBCS fields are specified using the EGCS keyword. The initial attribute must specify an EGCS field, a DBCS/EBCDIC mixed field, or an EBCDIC field.
The corresponding MFLD statement specifies ATTR=(,nn) where nn is 2 or greater.
The application program contains 2 × nn additional bytes preceding the data field.
When nn=2, the initial attribute is changed as shown in the following table according to the value of the two attribute byte sets (4 bytes) specified in front of the data field by the application program.

Table 1. Dynamic modification of a DBCS/EBCDIC mixed field
Attribute Byte	EBCDIC	EGCS	Mixed
40404040	EBCDIC	EGCS	Mixed
05014040	Mixed	Mixed	Mixed
0501C3F8	EGCS	EGCS	EGCS
C3F84040	EGCS	EGCS	EGCS
C3F80501	Mixed	Mixed	Mixed
0500C3F8	EGCS	EGCS	EGCS
C3000501	Mixed	Mixed	Mixed
C3000500	EBCDIC	EBCDIC	EBCDIC

When the initial attribute specifies an EGCS field and the application program specifies dynamic modification of the input control attribute to a DBCS/EBCDIC mixed field, MFS replaces the value of the programmed symbol for which the EGCS field is specified with the device default.