In the display file DDS code an INVITE on the record header ands condition it with an indicator.
In the RPG code MAXDEV(*FILE) INFDS(IODATA) for the workstation file. e.g.
FMSM640DF CF E WORKSTN
F MAXDEV(*FILE)
F INFDS(IODATA)

Code the IODATA data structure e.g.
D IODATA DS
D STATUS *STATUS

Change the EXFMT’s to be WRITE/READS. Before the WRITE seton the indicator that was used to condition the INVITE. After the READ check the condition of STATUS e.g.
Note 58 in