[avr-chat] Newbie : Avrdude, STK500 and high voltage programming

[Darren Inwood]

Hi list,

I'd like to program the RSTDISBL fuse on an AtTiny15L, which disables the external reset function.  The datasheet reckons that after I've done this, I won't be able to program the chip except with a high-voltage programmer.  This is the bit I need help with.  I've included my working in case it's helpful, sorry that it makes this a bit long and hard to read.

I tried a few unused AtTiny15L chips, and 'avrdude -c stk500v2 -p t15 -P /dev/ttyS0 -U fuse:r:fuse.txt:r' resulted in a file containing the character P, which hexdump tells me is 0x50.  So the existing binary is 0101 0000.

The datasheet says the bits are BODLEVEL, BODEN, SPIEN, RSTDSBL, two reserved bits and then CKSEL1..0.  To just set the RSTDISBL to 0, I put 0100 0000 or 0x40 back in using the command:

avrdude -c stk500v2 -p t15 -P /dev/ttyS0 -U fuse:w:0x40:m

This worked OK.  Now I was expecting to have a chip that would only go into programming mode with a high voltage (+12V) on the RST pin.  The STK-500 manual has a page on how to set up for this; I've set up the jumpers and routed the signals to the places they specify using the supplied cables.

When I try to program it now, it fails.  If I measure the voltage on the reset pin, it goes to +5V, not to the higher voltage I was expecting. The STK-500 manual hints that the unit itself controls the level of the reset voltage.

Is there anything furthur I need to tell avrdude to do, to ask the STK500 to use 12V instead of 5V for the RESET line?  I'm not entirely sure whether this is a hardware or software issue.

Also, the application that was on the chip previously does not run after writing the fuse bits, but I'm unsure of whether this is because the chip has been erased, or if I've just completely stuffed up my understanding of the fuse bits!

Thanks for any and all help,
--
Darren
NZ