A PC routine can receive control in either supervisor state or problem state. A PC routine must receive control in supervisor state if:

• The PC routine uses system services that are available only to programs that run in supervisor state. An example of such a service is the PCLINK macro.
• The PC routine can be invoked by a basic PC issued from a program that runs in supervisor state. This requirement exists because the system does not allow a basic PC routine that receives control in problem state to issue the PT instruction to return to a program that runs in supervisor state.

Otherwise, the PC routine can run in problem state.