AT90S8515 Failing to sink

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I'm a novice to programming microcontrollers. I've done some projects during my engineering education and found it very interesting, so I found my STK 200 kit with an AT90S8515 chip on, to start learning some more programming on my own.

I've written some small programs, for manipulating the LEDs on the board, using the cvavr c-compiler. After compiling and programming the chip, everything seems fine. The LEDs are blinking, but just for some seconds, sometimes allmost a minute, then it goes dark or only a few of the LEDs are blinking. After a while it sometimes starts blinking a few LEDs again. When I turn off and on it sarts OK but fails again after a short while.

When I measure the voltage on the Pins it seems like the 8515 is having trouble to sink. The voltage dropps only from 5,00 volt to 3.72 volt, measured with a Fluke 89.

Usually it seems like the program is still running, as the voltage goes to 3.72 volt when the LED was supposed to light, and back to 5,00 volt when it should turn off. but sometimes it stalls.

The short period it works, the voltage drops to 0.62 volt. I'measured both the supplyvoltage and the ground, and they both seems stable on 5.00 and 0,00 volts.

One thing I found a bit strange is that the controller resets when i measure the !reset pin.

Please! have anyone experienced this before? Anyone having an idea what might be wrong?

Kim

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Put a 4k7 pullup resistor (to +5) and a 100nF to ground on your reset pin to start. Also do you have any series resistor with your leds to limit the current? (around 680R will give about 5ma)

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Are all of the processor's ground pins connected to ground?

Normally, when a port pin cannot pull low, it means that there is too much current flowing.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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You shouldn't need any pullups on the reset pin.

If grounds are properly connected to the device, I would tend to believe you have not configured the port as an OUTPUT and are merely putting the port into HI-Z or PULLUP as an INPUT.

You must tell the DDR of the port to be an OUTPUT for the LED PIN. After which a 0 is ~0 and a 1 is 5v.

Set your DDR on powerup and then you can simply high or low the IO line.

Regards

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Quote:
You shouldn't need any pullups on the reset pin.
This could be troublesome in noisy environments :( The reset pin has an internal pullup but it's about 100-500K so probing it with the meter will cause a reset as described by Kim.

Quote:
After compiling and programming the chip, everything seems fine. The LEDs are blinking, but just for some seconds, sometimes allmost a minute,
This would indicate proper init, but if your leds do not have any series resistors, then the chip will try to source/sink too much current and it would probably get hot/shutdown/blowup. Also check that your stack is initiliased properly.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Thanks for quick and constructive response! :D

I use the STK200 AVR Starter Kit from Kanda Systems. According to their scheme for support circuits, the LED’s have a 1k Resnet in series. In the brownout detector circuit there is a pull-up resistor at 10k connected to Vcc.

According to the data sheet there are only one ground pin, pin 20. I use a 40 pin DIL.

My DDR is set for output, and I think the stack work properly as the voltage drops to 3,72 volts and back to 5,00 again when it should.

After studying the scheme from Kanda systems, I tend to think there is something wrong with the brownout detector circuit. Any of you having any experience with this circuit?

Kim