3270 display fields
Display data consists of a combination of characters to be displayed and instructions to the device on how and where to display them.
Under ordinary circumstances, this data consists of a series of field definitions, although it is possible to write the screen without defining fields, as explained in Unformatted mode.
After a write command that erases, you need to define every field on the screen. Thereafter, you can use a plain write command and send only the fields you want to change.
To define a field, you need to tell the 3270:
- How to display it
- What its contents are
- Where it goes on the screen (that is, its starting position in the buffer)