When the device releases the nRSTOUT pin, the
watchdog starts with the Long Window. This Long Window has a time interval
(tLONG_WINDOW) with a default value set in bits WD_LONGWIN[7:0].
As long as the watchdog is in the Long Window, the
MCU can configure the watchdog through the following register bits:
- WD_EN to enable or disable
the watchdog
- WD_LONGWIN[7:0] to increase the duration of the Long-Window time-interval
- WD_MODE_SELECT to select the Watchdog mode (Trigger mode or Q&A
Mode)
- WD_PWRHOLD to activate the
Watchdog Disable function (more detail in Section 8.3.10.4)
- WD_RETURN_LONGWIN to
configure whether to return to Long-Window or continue to the next sequence
after the completion of the current watchdog sequence (more detail in Section 8.3.10.4)
- WD_WIN1[6:0] to configure the
duration of the Window-1 time-interval
- WD_WIN2[6:0] to configure the
duration of the Window-2 time-interval
- WD_RST_EN to enable or
disable the watchdog-reset function
- WD_FAIL_TH[2:0] to configure
the Watchdog-Fail threshold
- WD_RST_TH[2:0] to configure
the Watchdog-Reset threshold
- WD_QA_FDBK[1:0] to configure the settings for the reference
answer-generation
- WD_QA_LFSR[1:0] to configure the settings for the question-generation
- WD_QUESTION_SEED[3:0] to configure the starting-point for the 1st
question-generation
The device keeps the above register bit values
configured by the MCU as long as the device is powered.
The MCU can configure the time interval of the
Long Window (tLONG_WINDOW) with the WD_LONGWIN[7:0] bits. The
WD_LONGWIN[7:0] bits are defined as:
- 0x00: 80 ms
- 0x01 - 0x40: 125 ms to 8 sec,
in 125-ms steps
- 0x41 - 0xFF: 12 sec to 772
sec, in 4-sec steps
Use Equation 3 and Equation 4 to calculate the minimum and maximum values for
the Long Window (tLONG_WINDOW) time interval when WD_LONGWIN[7:0] >
0x00:
Equation 3. tLONG_WINDOW_MIN = WD_LONGWIN[7:0] × 0.95
Equation 4. tLONG_WINDOW_MAX = WD_LONGWIN[7:0] × 1.05
Note: If the MCU software changes the
duration of the Long-Window to an interval shorter than the time in which the
watchdog has been in the Long-Window, the time-out function of the Long-Window does
no longer operate.
When the MCU clears bit WD_EN, the watchdog goes
out of the Long Window and disables the watchdog. When the watchdog is deactivated in this way, the MCU can set bit WD_EN back to
‘1’ to enable the watchdog again, and the MCU can control the ENABLE_DRV bit when no other error-flags are
set. The MCU must clear bit WD_PWRHOLD before setting bit WD_EN
back to ‘1’ to start the watchdog in Long Window.
The watchdog locks the following configuration
register bits when it goes out of the Long Window and starts the first watchdog
sequence:
- WD_WIN1[6:0]
- WD_WIN2[6:0]
- WD_LONGWIN[7:0]
- WD_MODE_SELECT
- WD_QA_FDBK[1:0], WD_QA_LFSR[1:0] and WD_QUESTION_SEED[3:0]
- WD_RST_EN, WD_EN,
WD_FAIL_TH[2:0] and WD_RST_TH[2:0]