Just how good is the brownout circuit on the various MSP430 parts (MSP430G in particular)? Particularly, in the face of very slowly rising gcc: can I use a solar panel and a supercap or battery connected directly to the power pins, and count on the CPU not waking up (held in reset by the BOR circuitry) until the voltage is at least high enough to ... check its own supply voltage? There are micropower voltage detectors that can do this (eg panasonic mn1381), but the BOR circuitry in many microcontrollers isn't as good.
westfwcan I use a solar panel and a supercap or battery connected directly to the power pins, and count on the CPU not waking up (held in reset by the BOR circuitry) until the voltage is at least high enough to ... check its own supply voltage?
The BOR circuit is a simple comparator with hysteresis. It detects whether voltage goes below lower threshold or exceeds upper threshold. But these thresholds aren't that precise. Assumption is that the additional delay due to the reset cycle is enough to reach a suitable VCC once it has passed teh BO-threshold. For slowly rising VCC (in the millisconds is considered slow), additional help by a reset pulldown capacitor and a pullup resistor is required, so that RST follows VCC, considering it low, until VCC stops rising.
But in your case, VCC will rise so slowly, that you'll need a supercap on RST too. An external comparator would be the best solution in your case.
Don't expect expensive high-precision components in a complex, but still very low-cost device. :)
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