"The B3 pin is optional and is not used for programming. However, the Monitor feature of the debugger does use B3. It is possible to program and debug (without monitor) and allocate B3 to the target hardware. In this case, do not connect B3 to the ICD connector. If the monitor feature is not used, userstream can be disabled in the configure tab and the connection from 1-6 does not matter. Although B3 is recommended, any PIC pin can be used for this feature.
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т.е. этот вывод служит чтоб по сигналу с назначеной ноги pica останавливать отладку ?