CICS : FSET and FRSET

FRSET(flag reset) turns off the modified data tag in the attribute bytes for all the fields on the screen before what you're sending is placed there.  (Once set on, whether by the user or the program, a modified data tag stays on until turned off explicitly, even over several transmissions of the screen.  It can be turned
off by the program sending a new attribute byte, an FRSET option, or an ERASE, or an ERASEAUP, or by the user pressing the CLEAR key.)  FRSET option is most often used in preparing to read new data
from a map already on the screen.  It can also reduce the amount of data re-sent on an error cycle

 FSET -Turns on the modified data tag.  This causes the field to be sent on the subsequent read whether or not the user keys into it.  If you don't specify this, the field is sent only if the user changes it.