Re: [avrdude-dev] Fusebit (RSTDISBL) on ATtiny15

[Jan-Hinnerk Reichert]

On Friday 12 December 2003 06:31, Brian Dean wrote:
> On Thu, Dec 11, 2003 at 11:15:28AM +0100, address@hidden wrote:
> > If I want to use PB5 as a "normal" I/O instead of RESET on a
> > ATtiny15 I have to program the RSTDISBL-fuse. But after that I
> > can't use the ISP (low-voltage) programming mode, right?
> > Currently I'm using Brian Dean's programmer. So, isn't it
> > possible to use this thing furhter on?
>
> Once you set the fuse bit so that the /RESET becomes an I/O pin,
> you can no longer access programming mode via the ISP.  If you have
> an STK500, or other programmer that supports parallel programming
> mode, you should still be able to program it that way, but the chip
> usually needs to be removed from the circuit for parallel
> programming.

The ATtiny15 does not support parallel programming (it's only 8-pin 
;-), but high-voltage serial programming. Unfortunately, the 
high-voltage serial programming is quite different from SPI ;-)

> > BTW: with what command can I program the fuse?
>
> In AVRDUDE, the easiest way to set fuse bits is to program them on
> the command line using the -U option:
>
>       avrdude -p <part> -U fuse:w:<value>:m
>
> Where <value> is the desired byte value of the specified fuse byte.
> There's currently no way to set an individual bit - you need to
> figure out what the fuse byte needs to be and set all the bits at
> once.  You can preced the <value> field with '0x' to use hex values
> which is generally easier to use to do bit arithmetic in your head
> than decimal.

This is the value that needs to be send as byte of the SPI-command 
(actually, there is some masking done on the value, but the bit 
positions remain the same)

> For displaying current fuse values, terminal mode is nice:
>
>       avrdude -p <part> -t
>       ...
>       avrdude> d fuse
>
> You can also set fuse values from here using the 'w' command
> (write).

This is the byte returned by the read command. Note, that for some 
chips (I don't recall which one) the bit positions in read and write 
may be different ;-(

/Jan-Hinnerk