The watchdog uses a 4-bit question counter (QST_CNT[3:0] bits in Figure 8-25), and a 4-bit Markov chain to generate a 4-bit question. The MCU can read this question in the WD_QUESTION[3:0] bits. The watchdog generates a new question when the question counter increments, which only occurs when the watchdog detects a good event. The watchdog does not generate a new question when it detects a bad event or a time-out event.

The question-counter provides a clock pulse to the Markov chain when it transitions from 4’b1111 to 4’b0000. The question counter and the Markov chain are set to the default value of 4’b0000 when the watchdog goes out of the Long Window.

Figure 8-25 shows the logic combination for the WD_QUESTION[3:0] generation.

Figure 8-26 shows how the logic combination of the question-counter with the WD_ANSW_CNT[1:0] status bits generates the reference answer-bytes.

(1) If the current value for bits (x1, x2, x3, x4) is 4'b0000, the next value for these bits (x1, x2, x3, x4) is 4'b0001, and all further question generation begins from this value.

Figure 8-25 Watchdog Question Generation