Go Down

Topic: ATMega1284P Issues (Read 2228 times) previous topic - next topic

Retroplayer

#15
Apr 13, 2013, 04:59 pm Last Edit: Apr 13, 2013, 05:13 pm by Retroplayer Reason: 1
Actually, using a 16.934Mhz oscillator makes for a more accurate buadrate division which means less errors:

Quote

Freq (MHz)       Buadrate    Notes
16.9344  115200         Used in CD-DA systems and CD-ROM drives; allows integer division to 44.1 kHz (384×44.1 kHz), 22.05 kHz, and 11.025 kHz. Also allows integer division to common UART baud rates up to 115200. Frequencies also used are 11.2896 MHz, 22.5972 MHz, 33.8688 MHz and 45.1584 MHz.


http://en.wikipedia.org/wiki/Crystal_oscillator_frequencies

(error rate of 3.7% at 16MHz vs. 2.0% at 16.934Mhz so still not 'perfect' but actually better than 16Mhz exactly.)

Tak - Refer to image. I simply used jumpers to connect the onboard 16Mhz resonator.

And a lot of great info. Ill surely look into that and post back. Much appreciated!

westfw

Quote
using a 16.934Mhz oscillator makes for a more accurate buadrate

Not if the bootloader was compiled assuming a 16MHz clock.  That will yield nearly 8% error, if I calculated right.

tack


Tak - Refer to image. I simply used jumpers to connect the onboard 16Mhz resonator.

And a lot of great info. Ill surely look into that and post back. Much appreciated!

I can't follow the connections from the photo, there are just too many long looping jumpers everywhere.

You've got an Uno with no MCU and then two breadboards, one with a 328 and another with 1284.

Are you trying to share the Uno 16mhz crystal with both of these? If so then you can't just pick up both sides on the crystal to both XTAL pins on each chip. On one you drive the crystal normally and on the other just link the crystal output to XTAL in of 2nd chip I believe.

Also bear in mind that the XTAL pins are the opposite way round on 1284 vs 328. On the 328 it's the low impedance pin adjacent signal pin. On the 1284 it's the high impedance XTAL pin adjacent The RX0 signal pin. This is one reason we had issues with serial uploads on 1284 without adequate ground rings or full swing oscillator; the high z XTAL pin on 1284 seemed to susceptible to capacitively induced interference from the adjacent RX0 pin.

Still out of sync. I guess I'll just scrap the 1284s. I don't have the resources to purchase an external programmer or whatever will work with these uC's. Oh well.

CrossRoads

Send me a chip, I'll install a bootloader and send it back.
PM for address.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

pito

Quote
I don't have the resources to purchase an external programmer or whatever will work with these uC's.

A bullet proved programmer costs you $3.22 inclusive shipping.
Search "ebay usbasp"

Go Up