My 8052 controls a sensor, scales it and sends the message serially with crc and BIT result every 5msec, so I need to test the chip every 5msec. then check the BIT to decide weather to accept the sensor reading or not.(very tight)

A BIT test will not tell you if the sensor is broke, which is just as bad as the uC being broken. A system test will.

On a system like this I would, based on knowledge do a test on statistical abberations, whether the uC or the sensor broke, the test would be valid.

Erik

Erik

Erik