The STM804TM6F: The reset output is open-drain, so it requires an external pull-up resistor to the logic supply rail — the output stays low during normal operation and goes high when the supply falls below threshold, holding the reset state for a minimum 140ms timeout after the rail recovers.
Cross-reference to STM804RM6F
The STM804RM6F shares the same package, reset type, output structure, timeout, and temperature range — the only difference is the threshold voltage (3.075V for the TM6F vs a different threshold for the RM6F variant). If your BOM calls for the STM804RM6F but stock is tight, the STM804TM6F drops into the same PCB footprint and pinout — just verify the threshold matches your monitored rail voltage before committing.