How does PCAS know my bearing, altitude and squawk code?

On XRX, the local bearing, or heading information displayed on the traffic screen, comes from the built-in compass. It is displayed in 10° increments. For both XRX and MRX, the local altitude comes from either the built-in altimeter or from your transponder encoder, if one is present, broadcasting, and within tolerance. The altitude from your transponder is always double-checked against the built-in pressure altimeter to ensure accuracy. If any discrepancies occur, the unit defaults to using the built-in altimeter. The local squawk code comes from your transponder’s encoder output, if MRX or XRX has successfully linked to your transponder. Otherwise, a code of “0000” is shown. The squawk code can be found on the General Information page in Admin mode (XRX) or on the Local page (MRX).