no clock on Atmega328p-AU

Other Hardware General Electronics
1

Hi all,

I've just assembled a new board using an SMD processor for the first time (http://be.farnell.com/atmel/atmega328p-au/mcu-8bit-avr-32k-flash-32tqfp/dp/1715486) Atmega328P-AU.

Until now, I've always worked with DIP-28 version, so I'm familiar with that. For this particular design however, I needed to go SMD because of space restrictions. I have never tried to upload either the bootloader or a sketch through the ICSP header, but for this project it will be the way to go, so I've put that on the print as well.

The problems begins earlier, but I might be overlooking something obvious. I have installed only the following things:
-The processor itself, 5V on pins 4,6 and 18, GND on pins 3,5,21.
-a 10k resistor to the 5V on pin 29.
-a 16Mhz crystal between pin 7 and 8, and both with a 22pF cap to GND.

There are other traces on the PCB of course, but I haven't connected them to make finding the problem easier.
When I look with my scope on either pin 7 or 8, I get no clock. I'm used to see a 16Mhz sinus on the DIP-28 package, but I see absolutely no activity here.

The processor is straight out-of-the-box, so no bootloader/sketch has been loaded yet. Is it maybe using it's internal 8Mhz oscillator or something like that?

Any ideas would be greatly appreciated!
Thanks!
Jens

2

You always need decoupling capacitors - 0.1uF ceramic for each power pin. These
are not optional components and if omitted the device may malfunction (or not, or
sometimes work sometimes not, with mysterious and confusing symptoms....)

Factory chips do indeed use 8MHz internal RC oscillator - programming the bootloader
also sets the various fuse bits to specify clock source and brown-out voltage.

The first step is to load a bootloader using an ICSP (perhaps Arduino as ISP) -
The standard ArduinoISP sketch loads the bootloader and Blink sketch, so I'd
recommend adding an LED/resistor to Arduino pin 13 (package pin 17) - then you
can see the download progressing and see the Blink sketch working.

3

Excellent, thanks for the quick reply.
If the chip is using it's internal 8Mhz, would I still have to be able to see this on a scope on pins 7/8, or do these come not into play in that configuration?

4

jensvanhoof:
If the chip is using it's internal 8Mhz, would I still have to be able to see this on a scope on pins 7/8

No.

5

I think the factory default has those pins as general I/O.

6

Ok excellent, that makes sense.
I'll try to program the bootloader through the ICSP header asap.

Jens