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My SuperPro board in my controller, doesn't always initialize when external power is applied to J4. It always works when powered through the USB dongle. I can't get to the reset button to reset it after power-on, I need to insure that the board initializes when power is applied.

Are you sure your power is coming up cleanly, and with a good fast rise-time?

Jittery supply switching can muck things up pretty bad. A mechanical switch on the DC leg is about the worst way to turn power on and off. Switching the AC side of a ac/dc power supply is usually fine.

Lloyd

The power is from a 12 Volt battery source through a DC-to-DC converter that regulates it to 7.0 Volts, and that is connected to the J4 connector. I experience the problem when I connect to a 12 Volt stack of AAs or switch on the 12 Volt vehicle power. There are some pull-up resistors on the 5 Volt line.

Do I need some Delay to the Reset line?

Hmmm... I assume the 7V output is directly connected to J4 without a switch?

Did you put a de-glitching cap across that 7V line? Some high-frequency converters will issue a jittery spike upon power-up, and de-glitching is the solution. Probably something under 0.1uf will do the trick, but you might look at the specs on the converter to make sure. I have them on my mother boards, and they (for instance, MuRata converters) require an external output cap.

I have never used the reset line on the SuperPro. I just power it up (cleanly, of course), and it resets reliably.

I just saw your statement, "There are some pullups on the 5V line".

Pullups for what, drawing how much current? Are they just logic-level pullups, or are they driving loads? Are these references for inputs? If so, consider using the 3.3V supply for your logic level references. And don't forget that the LPC1756 has programmable pullups on-chip.

Have you checked the actual voltage on the board when it's fed from your converter, as opposed to that voltage when running off the USB supply? Check at the output of the 5V regulator on the SuperPro.

Could it be that your converter is running low under load?

Lloyd

I like the OKI-78SR for 12V battery operation, they have a wide range of input voltage 7-36V so they are pretty robust, and it wouldn't take a lot of protection in an auto environment. I know there are others out there using our controllers in automotive environments and can comment with first hand experience.

What size pullups and what are they pulling to, and what is the state of the power supply at the time. Many of these little micros can be "powered" from their inputs as there are parasitic diodes in most push pull IOs. It is possible the part is never really turning off and hence not getting a good reset. It might be experiencing a brown out which you can also detect.

Also if you have big caps on the supply it could take a long time to discharge, which can affect turn on.

We really need more details on you actual configuration. A scope to trace on the supply with a long measurement time might give you a clue. The LPC1756 does have a RESOUT pin (on pin 11), although I did not hook it to a via, it should still be probable.

Many of these little micros can be "powered" from their inputs as there are parasitic diodes in most push pull IOs. It is possible the part is never really turning off and hence not getting a good reset.
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Wow... Bingo! And I completely forgot about that! Shucks! You can even power LS-TTL that way, if you're not careful!

LLoyd