ATMEGA644A-AU strange clock speed

Other Hardware 3rd Party Boards
1

I have made on a breadboard a project using ATMEGA644-20PU (16MHz crystal and 22pF capacitors) and I programmed the microcontroller using Arduino uno as ISP (I used Arduino 1.6.5 and I installed the Sanguino platform at the following URL https://raw.githubusercontent.com/Lauszus/Sanguino/master/package_lauszus_sanguino_index.json). Everything worked fine.

Now I have made a PCB using ATMEGA644A-AU (16MHz smd crystal with 22pF capacitors). I am able to program successfully the microcontroller with the same software configuration described before. However, I notice that the CPU speed is much less than 16MHz (when I run a sketch testing the serial communication I notice that the true baud rate is 600baud/s instead of 9600 baud/s). Moreover, when I run a blink sketch I notice that the blink time is different form what I expect.

I have also replaced the smd crystal with the through-hole crystal I used in breadboard but nothing has changed.

How to fix the problem? Should I sobstitute the ATMEGA644A with ATMEGA644P?

Thanks in advance

2

You need to set the fuses by selecting the appropriate board, connecting ISP programmer, and doing 'burn bootloader' (even if you're not using a bootloader - the bootloader (if any) will be overwritten if you then program via ISP, but the fuses will not be) - this will set the fuses, which, among other things, tell it what to use for the system clock.

Since you haven't done that, it's using the default option - 8mhz internal clock divided by 8 to get a 1mhz system clock. Hence all the time keeping is going at 1/16th the expected speed :wink:

You can also do this using avrdude from the command line, or a tool like eXtremeBurner AVR (windows tool for USB Asp programmer)