To pass parameters to your program, append them to the ASMIDF command
after a slash (⁄). IDF interprets anything that follows a slash as
parameters that should be passed to the target program.
The parameter string is passed to the target in standard z/OS®
EXEC PGM style. That is, R1 points to a word that points to a halfword length field
that is followed by the parameter string itself. Figure 1. Specifying parameters for your program (TSO)