You can specify the encoding in which the resulting 3270 data stream is to be constructed. When the terminal is installed, the CICS® server (providing it supports EPI Version 2) is informed of the encoding applied to the 3270 data stream. If you specify null, the encoding used by the CICS Transaction Gateway server is used (or the default encoding of the application if the local gateway is being used).
Basic terminals always work in the encoding used by the CICS Transaction Gateway server (or the default encoding of the application if the local gateway is being used).
Refer to your CICS Server document for more information on supported code pages.