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gertc
Joined: 06 May 2006 Posts: 88
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Posted: Wed Aug 27, 2014 1:23 am Post subject: Setting Fuse bit |
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Hello,
I want a pretty accurate low frequency output on a specific pin using Timer0 using an ATTINY84, so I tried to see what happen when changing the fusebit from 8Mz internal clock to 128Kz. Now I can't reverse it. Chip can't be recognized........
Are there anything I can change in the AVR environment so I can change it back to the 8Mz internal clock?
Using ver. 2.0.7.7 and STK500 programmer.
thanks,
gerryc
(BASCOM-AVR version : 2.0.7.7 ) |
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jenalcom
Joined: 10 Apr 2004 Posts: 365 Location: Perth, Western Australia
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Posted: Wed Aug 27, 2014 3:53 am Post subject: |
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Try injecting a cloxk signal (say 1MHz) into XTAL1 of the chip. Hold it there while you reset and reprogramme the chip then you should be OK |
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MWS
Joined: 22 Aug 2009 Posts: 2262
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Posted: Wed Aug 27, 2014 6:33 am Post subject: |
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jenalcom wrote: | Try injecting a cloxk signal (say 1MHz) into XTAL1 of the chip. Hold it there while you reset and reprogramme the chip then you should be OK |
If actually an internally low speed clock is selected, that won't help, as the controller does not accept any external clock then. Such is only useful, if mistakenly an external clock source or crystal was fused.
In this case, it depends on the capabilities of the programmer, as the ISP-clock needs to be not higher than 1/4 of the controller's clock. This means an ISP-clock of 32 kHz, and worse, if the CLKDIV8 fuse is still set, 4 kHz clock.
That's a challenge for the programmer, most cheap clones can't do that. |
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albertsm
Joined: 09 Apr 2004 Posts: 5913 Location: Holland
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Posted: Wed Aug 27, 2014 9:30 am Post subject: |
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use a working processor to create the clock signal. and indeed use a low frequency.
if that does not work your only other option is the parallel programming method. (or jtag when enabled/available) _________________ Mark |
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MWS
Joined: 22 Aug 2009 Posts: 2262
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Posted: Wed Aug 27, 2014 11:25 am Post subject: |
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albertsm wrote: | use a working processor to create the clock signal. and indeed use a low frequency. |
If the TO succeeded with:
Quote: | so I tried to see what happen when changing the fusebit from 8Mz internal clock to 128Kz. |
he can feed in a clock-signal till he get old and grey, as the Tiny84 128kHz RC oscillator is internal.
How do you think an external clock signal will convince the µC to suddenly get off the 128kHz internal clock?
If in contrary the TO has mistakenly set the fuse to external crystal or external clock, then it does not have to be low frequency, 1MHz or whatever is at hand is just fine.
AFAIR, if it's an original Atmel STK500 kit, in AVR-Studio 4 (or higher) the ISP-frequency for the programmer can be set as low as 4kHz, which should work in this case. |
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albertsm
Joined: 09 Apr 2004 Posts: 5913 Location: Holland
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Posted: Wed Aug 27, 2014 4:38 pm Post subject: |
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Quote: | How do you think an external clock signal will convince the µC to suddenly get off the 128kHz internal clock? |
you could tell it that you will increase the voltage to 12V if it will not change its bit but serious, no that will notl not work in this case, i missed the fact that he chosen internal osc. Only parallel programming method can change it in this case since it has no jtag. It is mentioned in the datasheet under memory programming. using stk500 should work fine. _________________ Mark |
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gertc
Joined: 06 May 2006 Posts: 88
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Posted: Thu Aug 28, 2014 9:45 pm Post subject: |
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Thanks for the suggestions.
I was able to change it back to 8Mhz internal clock
In Studio 4, I changed the ISP clock to 1.21Khz, where after I was able to changed the Fuse Bit using STK500.
thanks again,
gerryc |
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