The CMP option specifies the kind of compare operation to be used for sort/merge control fields up to 16 bytes long with the format PD or ZD. CPD may use the compare decimal instruction, and CLC uses the compare logical instruction. PD or ZD fields longer than 16 bytes automatically default to CMP=CLC.
The delivered default, CMP=CPD, provides a more efficient way of comparing records than CMP=CLC. However, if there is invalid data in the zone portion of a ZD field when CMP=CPD is used, the zone fields will be changed as a result of unpacking. If there is invalid data in either a ZD or a PD field when CMP=CPD is used, an OC7 abend may occur.