Is there a Atmega Chip with NO SPI Disable Fuse Option?

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I am new to microcontroller programing and I have lost couple of chips due to Fuse settinsg while creating SPI interface in my microcontroller circuit. Yesterday I was watching a video from eev video blog where author was saying that he loves PIC chips due to the fact that no fuse settings in PIC would disable the ISP - SPI interface. So at any time you can program your chip in circuit. I know that these chips can be reset using parallel programmer. But this question came to my mind that I saw a PEN pin on Atmega128 which enables ISP-SPI programming. So if this pin is dedicated programming enable pin does this mean that no matter fuse settings are done it would not disable ISP-SPI for the Atmega128 ?
If not is there any microcontroller chip in Atmega where there no fuse bit would disable the in circuit programmer interface ?

Wouldnt a chip with permenent in circuit enabled a great boon for newbies ?

regards

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None of the AVRs with 40 pins or more have RSTDISBL. It's only one the small chips where the chances are that you need every one of the 6/8/14/20/28 pins.

You have misunderstood the purpose of PEN in a m128 by the way - search here - there are loads of threads that discuss it.

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Thanks for your quick reply. I would search forums form PEN pin.

Quote:

None of the AVRs with 40 pins or more have RSTDISBL. It's only one the small chips where the chances are that you need every one of the 6/8/14/20/28 pins.

So does it mean that 40 Pins AVR would not loose in circuit programming ability no matter if fuse settings are wrong also ?

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Quote:

So does it mean that 40 Pins AVR would not loose in circuit programming ability no matter if fuse settings are wrong also ?


Not totally (though it's quite tricky to achieve). However many of the large chips have JTAGEN and almost all AVRs have SPIEN. You cannot usually change SPIEN using ISp but you can with JTAG. So you might disable ISP that way. In theory this wouldn't matter if you then just use JTAG.

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I find this question interesting, as you normally ( as cliff tolled) cannot disable the SPIEN fuse using ISP.

I know though that when I started (long long time ago..) I had managed to brick a mega168. It happend when I had programming speed way to high and then tried to change the fuse bits... in the end ISP was disabled.

I am curious as to what you did to brick the chip and if you checked if not accidentally you selected the wrong xtal and as such seem to have bricked the chip....
tell us a bit more, as at this point it might be that you are still able to recover....
and what chip and package

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I know though that when I started (long long time ago..) I had managed to brick a mega168. It happend when I had programming speed way to high and then tried to change the fuse bits... in the end ISP was disabled.

Most likely DWEN was inadvertently enabled.

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Well the bricked chip doesnt read , I dont have parallel programmer or JTAG programmer with me so dont know exact what Fuse bit got written in the chip. But I was trying to build a circuit with ISP connector and used the programmer which had came with Atmega8 developement bord made by a local shop. I had made connection to ISP according to standard pinout got on internet. But I found that for some reason the programmer had reversed MISO & MOSI in that PCB. Since he had also reversed it in his developement bord it was working fine with the developement bord. But when connected to my new circuit bricked the chip. Thats all I know. So now I have changed temporarly the ISP connection s in my circuit according to the programmer I have. But this cost me lots of time and efforts.

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I don't know how many AVR's I have used for dev. but I don't think I ever have killed one!!!
Yes I have tryed to flip + and - but they "tell" you quickly that they don't like it, and normally surrive but sometimes they need to rest (internaly cool down I guess 10 min or so).
Just flip MISO & MOSI should not kill anything.

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I guess a programmer would be protected against this but if you switch MOSI and MISO you likely have two outputs facing one another. If one drives Gnd and one drives Vcc then you have a potential high current short. As I say I guess programmers have current limiting resistors to prevent this but I wonder if all designs of programmer do?

One thing I'm not entirely clear on here by the way is exactly what chip we're talking about. The first post mentioned m128 but later there are mentions of m8.

If it's a mega128 the big "gotcha" is that the ISP pins are not the SPI pins (as expected in almost all other AVRs) so if attempts were made to connect ISP to SPI it wouldn't work.

If it's a mega8 then the only "serious" (non hardware) damage that could be done would be if RSTDISBL had been set. Otherwise the chip should be recoverable.

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clawson wrote:
None of the AVRs with 40 pins or more have RSTDISBL.

ATMega169P :twisted:

No RSTDISBL, no fun!