The programmer needs to ensure that any data files they read are in the character set that matches the program. The File Handler will issue an abend if it is asked to open a file whose catalog entry has a different character set from the character set of the program.
In-stream data and line sequential files are automatically converted to match the mode of the application program. Data in all other files is not converted.
All data presented to or exchanged with the program is either ASCII or EBCDIC depending on the character set of the program. Conversions are done as appropriate. This includes data in MVS control blocks.
Pointer data is native unless AMODE is in effect, in which case, it is big-endian (network order). This includes data in MVS control blocks.
Binary data is always big-endian. This includes data in MVS control blocks.