Hi,

I recently did a project with tehy MSP430F413 which has onboard brown out
detection (BOD) and also an onboard watchdog timer.  But both are software
enabled by the code and are not active at initial power up.  They are only
active after the device successfully boots and runs the startup code.

The result was that my target always booted correctly off the FET module but
only started correctly 80% of the time when booting stand alone.  The power
supply was a conventional transformer with rectifier, filter capacitor and
linear regulator with bypass capacitors.  Other things also ran off the
pwoer supply so it was convenient to also use it for the MSP430 circuit.

The cause was the unpredictable startup of the MSP430 if the device has a
slowly rising power supply (ie. starts in the browned out condition and
transitions through it slowly).

The cure was an external supervisor to hold the MSP430 in rest until the
power supply was within tolerance.

This is in contrast to the BOD circuits on some other parts (PIC, Atmel AVR)
which are enabled as a hardware feature and can be active at power on rather
than after software boot.

So it is worth looking at the circuit, the part being used and working out
what is needed.  For non-mission critical subsystems I am OK with a software
enabled hardware watchdog but the BOD or power up circuit has to be active
at power on.

Ray

On Thu, 25 Mar 2004 12:20:33 +1100, you wrote:

>So it is worth looking at the circuit, the part
being used and working out
>what is needed.  For non-mission critical subsystems I am OK with a software
>enabled hardware watchdog but the BOD or power up circuit has to be active
>at power on.

Hehe.  Of course, I've actually used a PIC12F629 as a "POR/BOR
and external WDT, with debounced manual reset input" device for
the MSP430.

Sad, that.

Jon