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bahman
11-03-2005, 07:13 AM
Hi friends,
I am new in microcontroller and your forum as well.
I bought a STK500 with preprogrammed mega8515 that works well in the STK500 board.
But when I use this micro out of Stk500, in a breadboard with XTAL and 2 capacitors, it doesn't work (one Switch and one LED).
I think the circuit is very very simple, but I don't know why it couldn't work.
Do you have any advice?
Thanks

EmbeddedGuy
11-03-2005, 10:33 AM
Hello,
Using logic probe check activity of xtal. Check power supply voltage and connections to microcontroller pins.

Bye

Supario
11-03-2005, 03:15 PM
Hi,

Make sure the crystal is very close to the XTAL1 and XTAL2 pins on the microcontroller (ie in the adjecent hole) and that the leads of the two capacitors (22pF ceramic) are as short as possible.

EmbeddedGuy
11-03-2005, 04:18 PM
Hello,
Yes xtal should be as close as possible to microcontroller. Check the activity of xtal by logic prob, if does not show any activity check two 33pf caps. it may be short or open. If still it refuses to oscillate try xtal oscillator, some times good xtal does not oscillate due to some problem in internal amp. of microcontroller. It also happens with me using PIC16F84A. Xtal osc. is good, it is very stable and gives clean TTL output signal. Although it is costly. Normally I try to use xtal osc.

Bye

bahman
11-04-2005, 01:52 AM
Hi and thanks for your help.
I don't have any osciloscope to see the activity of XTAL. But I cheked the power supply and it shows OK and 5 volts. The voltage on the XTAL shows me around 2 Volts which may be shows XTAL activity.
I made both leads af XTAL and capacitors as short as possible and near to the Micro but it doesn't work, I changed the Xtal from 4MHZ to 10 as well, but nothing happened.
Thanks again
Bahman

EmbeddedGuy
11-04-2005, 06:47 AM
Hi,
I suggest you to try xtal osc. I think internal amp is not working properly, as I told you this also happens with me but on PIC16F84A. When I given 4Mhz clock using xtal osc. it work. Try xtal osc. Use high speed logic probe about 20Mhz.

Bye

ice
11-04-2005, 08:27 AM
Did you pull the "Reset" pin high.
If its low or floating,it might not work.
Check all your grounds.

vkp
11-05-2005, 10:37 AM
hey few time, i have experienced that new xtals not working (bad luck).
so try changing it.
also important is to check the components at reset pin.

at reset pin, one resistor to the Vcc and one capacitor with ground. make it sure.

all the best

bahman
11-06-2005, 10:05 AM
Hi guys
Thanks. It is working.
I did all suggestions together, xtal as close as to pins-changed xtal-reset resistor to high....
Thanks again
Bahman

EmbeddedGuy
11-06-2005, 03:40 PM
Hi,
Congrats for your success. I wish best of luck for your ongoing project.
Bye