ARM7 power shutdown question

[dani]

Hello all,

I am using following code to shutdown the ARM7 AT91Sam7128 chip. If i do not give much delay(i.e. more then 1sec lets say) and apply the power source again. The microcontroller seems to be halt some how. If any one can help me to get through this problem i will be very grateful.

(void) AT91F_RSTSetMode( AT91C_BASE_RSTC, 0);
// Sets the a pin low, for shutdown, this pin disables the vcc source
GPIOOutputPortLow(AT91GPIO_SHUTDOWN);
//
while(1)
{
TimersWatchdogReset();
}

Regards
Dani

 

[mjbcswitzerland]

Hi Dani

You may need to check the power supply slew rate when turning on again:

See **broken link removed**

Less that 6V/ms can cause the processor not to start (see also **broken link removed** )

Regards

Mark

NO SIGNATURE LINKS ALLOWED

 

[bobsanjose]

Hello all,

I am using following code to shutdown the ARM7 AT91Sam7128 chip. If i do not give much delay(i.e. more then 1sec lets say) and apply the power source again. The microcontroller seems to be halt some how. If any one can help me to get through this problem i will be very grateful.

-snip-
Regards Dani

Hi,
I assume with shutdown you are really switching off the power to the board / MCU! If so, power does not return to "0" or even a low level until all the Caps on the board have discharged. Depending on your caps and many other things, this can take anywhere from a few usec to several minutes. Often larger caps are used to reduce the more powerful noise peaks. Check your supply voltage with a scope when your program switches the power off. How low does it have to go before the power on sequence will execute successful again. Make sure it is turned off that long. You can also insert some bleeders, pull-down resistors (transistors) that will empty your caps much faster but they also contribute to the overall power consumption.
Most likely your voltage is within an undefined range when you apply power again and the MCU freezes up.

Other sources of this behavior possible, but this one has a good chance to be the culprit.

Hope this helps, Bob
btw. has nothing to do with ARM7 but probably everything to do with board layout