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3. Device may lock for further programming
Special combinations of fuse bits will lock the device for further programming effectively turning it into an OTP device. The following combinations of settings/fuse bits will cause this effect:
– 128 kHz internal oscillator (CKSEL[1..0] = 11), shortest start-up time
(SUT[1..0] = 00), Debugwire enabled (DWEN = 0) or Reset disabled
RSTDISBL = 0.
– 9.6 MHz internal oscillator (CKSEL[1..0] = 10), shortest start-up time
(SUT[1..0] = 00), Debugwire enabled (DWEN = 0) or Reset disabled
RSTDISBL = 0.
– 4.8 MHz internal oscillator (CKSEL[1..0] = 01), shortest start-up time
(SUT[1..0] = 00), Debugwire enabled (DWEN = 0) or Reset disabled
RSTDISBL = 0.
Problem fix/ Workaround
Avoid the above fuse combinations. Selecting longer start-up time will eliminate the problem.
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