Changing clock source in AVR?

I have a Olimex devboard AVR-P28B with a ATMEGA8 on it. I programmed and used it just fine when it was running on the internal RC oscillator. But I wanted to try to get it working on the 4Mhz crystal so I set the fuse bits and wrote those. Problem is, now it doesn't work anymore and I can't get it to respond and change the fuse bits.

How can I program the fuse bits in this situation? I assumed that the programming interface always runs off the RC-clock otherwise a wrong write could render the device useless but I think that's not the case.

LV

*** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from
formatting link
***
Reply to
Lord Vain
Loading thread data ...

it

It IS the case. the only way to get the AVR talking to the programmer is to apply a clock from an external source to the AVR.

Meindert

Reply to
Meindert Sprang

external clock means a HCMOS signal, not a crystal. The fuses are written as zeroes, not as ones.

Rene

--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
Reply to
Rene Tschaggelar

High Voltage Parallel Programming with an STK500 always works.

Mit freundlichen Grüßen

Frank-Christian Krügel

Reply to
Frank-Christian Kruegel

I

bits

it

write

I'm using STK200. Does that mean I'm fried or should that work too?

*** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from
formatting link
***
Reply to
Lord Vain

I

bits

write

to

Weird. Any ideas why it isn't working then? I'm using YAAP and an Olimex parallel port programmer. I also tried programming it using AVRDUDE but that didn't work either.

*** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from
formatting link
***
Reply to
Lord Vain

The ATMEGA8 reset pin can be programmed to be a normal I/O pin. Once you have done that, I do not think there is any way to program it again. (Ponyprog used to have a bug where if one read the ATMEGA8 fuses, and wrote the same values back, the reset pin was set to I/O. I lost a couple of devices before realising it)

Regards Anton Erasmus

Reply to
Anton Erasmus

I

bits

it

write

I just messed around with the fuses. I'm pretty sure I didn't set the reset pin to a I/O.

BTW I can see data going over the MOSI and MISO lines on my scope yet the programming software (YAAP en AVRDUDE) says there's no device at the other end!

*** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from
formatting link
***
Reply to
Lord Vain

You're fried. Only the STK500 can do HVPP. This doesn't work through SPI, but through the regular port pins, which change functions when pulling /RST to +12V. The STK500 has sockets for this.

Mit freundlichen Grüßen

Frank-Christian Krügel

Reply to
Frank-Christian Kruegel

/RST

On the Olimex forum I read that I need to apply a clock (or square wave) to the XTAL1 input to get the thing going. Otherwise I'll need a HVPP programmer (such as Atmel's STK500 Starter Kit) to program the device.

However, I also remember that setting the 'Startup time' to 'fast' and I wonder if that could be the problem since I can't understand that me setting the oscillator to external crystal will hang the device that's not logical.

Why didn't Atmel just let the ISP interface *always* run off the internal oscillilator, thereby elliminating these problems?

*** Free account sponsored by SecureIX.com *** *** Encrypt your Internet usage with a free VPN account from
formatting link
***
Reply to
Lord Vain

you set the wrong fuse. You will need a external function generator or something like that to run the pins directly.

Reply to
DAC

Because this wouldn't rule out other user errors. Example: Some devices allow to switch /reset to a normale port pin, disabling ISP programming. There is even a fuse for disabling ISP completely, which cannot be set by ISP itself, but through user software.

It's not Atmel's fault if users buy unsuitable tools just for saving some $$$/¤¤¤/¥¥¥/£££. Remember: HVPP always work no matter how the fuses are set.

Mit freundlichen Grüßen

Frank-Christian Krügel

Reply to
Frank-Christian Kruegel

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.