The VV command is designed to vary the access mode of a VTS that has been initialized in read-only mode — that is, where the TSRACCESS option is set to RO. The VTS name must be specified in the TB-SUBSYSTEM field of TB-PARM, and the desired operation is determined by a request ID supplied in the FUNCTION-ID field of the COMMAND-AREA.
When a VTS is swapped to read-write mode via the VV command, the job performing the swap acquires a read-write lock on the VTS. No other job or region can access the VTS while this lock is held. The VTS remains locked in read-write mode until it is explicitly swapped back to read-only by the same job step that holds the lock.