The scanner interface trace, a joint function of VTAM® and the NCP, stores the operating parameters of a line whenever a 3720, 3725, or 3745 communication controller sends or receives a message. Although the trace is controlled by VTAM, the information in the trace records is collected by the NCP. The scanner interface trace collects the operating status of a line whenever the communication controller sends or receives a message (PIU).

When you start the trace, you can choose how many bytes of data you want to trace. The default is the entire PIU. You can use the scanner interface trace only on lines operating in network control mode.

For each communication controller, a combination of eight line traces or scanner interface traces can be active at a time. The number of active scanner interface traces to be allowed is specified during NCP generation (default is 2). In a multisystem network in which the communication controller is connected to more than one host processor, the number of active traces allowed is distributed among the connected host processors on a first-come, first-served basis.