PU

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   .-PU--=--YES-----.   
>>-+----------------+------------------------------------------><
   |        .-YES-. |   
   '-PU--=--+-----+-'   
            '-NO--'     

Specifies whether a BSC 3270 is treated as a physical unit and whether all terminals subordinate to the cluster are treated as logical units.
PU=NO
If PU=NO, it is assumed that the associated terminals are supported by a line control program such as the IBM® licensed program Network Terminal Option (NTO) or a similar user-written program.
PU=YES
If PU=YES, the device type must be a 3270 type.

You cannot code this operand on the CLUSTER definition statement. You must code it on the GROUP or LINE definition statement, and let it sift down to the CLUSTER level.