DocID025336 Rev 1

9/23

AN4370

Flashing an external microcontroller

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Flashing an external microcontroller

The watchdog inside the L99ASC03 acts on both the NRES pin and the VDD pin.

In case these pins are connected to an external microcontroller, then either the watchdog

has to be disabled or the connections have to be removed before flashing the

microcontroller.

To flash the microcontroller, one of the following techniques could be chosen:

1.

Put the L99ASC03 in VDD Standby Mode with ICMP = 1 and then download the

microcontroller firmware. Care must be taken in order not to wake up the device from

VDD Standby Mode (via SPI frame or INH high).

Since the watchdog is disabled in VDD Standby Mode when ICMP = 1, the device will

not act on the NRES pin and on the VDD pin while the firmware code is downloaded

into the microcontroller.

2.

Put the L99ASC03 in Flash Mode and then download the firmware.

Regardless of its operating mode, the device can be put in Flash Mode by applying a

We recommended connecting the BC input pin to GND if not used or to a

microcontroller GPIO if used, to update the BEMFCNT in block commutation mode.

3.

Remove the NRES connection between the microcontroller and the device, power the

microcontroller through an external 5V source and then download the firmware.

During the download process the device will most likely enter in VBAT STDBY mode

due to missing WDG trigger, hence the device will have to be woken up from VBAT

STDY mode after the programming phase. Once programmed, the NRES and VDD

connections will have to be restored and the system rebooted.