SLLSFZ8 November 2025 MCF8329HS-Q1
PRODUCTION DATA
MCF8329HS-Q1 provides an external watchdog feature to monitor the health of an external MCU - EXT_WD_EN bit should be set to 1b to enable the external watchdog. When this feature is enabled, the device waits for a tickle (low to high transition in EXT_WD pin or WATCHDOG_TICKLE set to 1b over I2C) from the external watchdog input for a configured time interval; if the time interval between two consecutive tickles is longer than the configured watchdog wait time, a watchdog fault is triggered. The watchdog fault response can be configured using EXT_WD_FAULT_MODE and LIMP_HOME_EN as shown in Table 7-6. When LIMP_HOME_EN is set to 0b (limp home mode disabled), fault response is either report only (FETs active and driving motor at input reference) or latched (FETs in Hi-Z) depending on EXT_WD_FAULT_MODE. The latched fault can be cleared by writing 1b to CLR_FLT or by issuing a tickle on EXT_WD pin or over I2C. When LIMP_HOME_EN is set to 1b (limp home mode enabled), fault response is either the input reference latched to current value or latched to REF_OFF1 depending on EXT_WD_FAULT_MODE - MCF8329HS-Q1 operates the motor at the latched input reference till 1b is written to CLR_FLT or a tickle is issued on EXT_WD pin or over I2C. Once the watchdog fault is cleared (by writing 1b to CLR_FLT or by issuing a tickle on EXT_WD pin or over I2C), MCF8329HS-Q1 exits the limp home mode and drives the motor to the input reference from the reference source configured by SPEED_MODE (analog, PWM, I2C or frequency). When a watchdog timeout occurs, WATCHDOG_FAULT bit is set to 1b. In case the next tickle arrives before the configured time interval elapses, the watchdog timer is reset and it begins to wait for the next tickle. This can be used to continuously monitor the health of an external MCU (which is the external watchdog input) and place the MCF8329HS-Q1 in a known state, in case the external MCU is in a fault/hang state.
The external watchdog input is selected using EXT_WD_INPUT_MODE and can either be the EXT_WD pin or the I2C interface. The time interval between two tickles to trigger a watchdog fault is configured by EXT_WD_CONFIG; there are 4 time settings - 100, 200, 500 and 1000ms for the EXT_WD pin based watchdog and 4 time settings - 1, 2, 5 and 10s for the I2C based watchdog.
When a watchdog fault is triggered (irrespective of EXT_WD_FAULT_MODE and LIMP_HOME_EN), an active low signal is available on the nMCU_RST pin to reset the external MCU as shown in Figure 7-52. The duration of this active low signal can be configured by nMCU_RST_TIME - 1ms or 10ms. MCF8329HS-Q1 waits for EXT_WD_CONFIG from the end of the active low signal duration before issuing another reset signal. During normal operation (no watchdog fault detected), nMCU_RST is pulled up to AVDD through an internal pull-up resistor.