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  Home >> News & Events >> ISP programming not working
ISP programming not working

Author:  From:  Date:2011-3-1

Why doesn't ISP programming work on my AVR?

If you are unable to ISP program your part probably one of the following has happend:

You have fused the AVR to a clock that is not present or running.

You have disabled the ISP interface by unprogramming the SPIEN fuse

You have programmed the RSTDISBL fuse (note this fuse is not available on all AVR parts)

You have enabled debugWIRE by starting a debug session or programming the DWEN fuse. Please see this FAQ entry to find out how to disable debugWIRE.

All of the above actions will lead to that the ISP interface is no longer working.

The only way to get out of this "mess" and reenable the ISP programming interface is to change the fuse configuration for your AVR part using High Voltage Programming. Please note that if your AVR microcontroller is new and the fuse bits have never been programmed before, your AVR has the default fuse setting as explained in the 'Memory Programming' chapter in the device specific datasheet.

Additionally, the following conditions may be causing problems when doing ISP programming:

You have altered the CPU clockspeed on your device so that the ISP programming frequency is no longer less than 1/4 of the target CPU frequency.

(AVRISP only) Not enough power on the target. The AVRISP uses target power to program the part. The AVRISP will draw maximum 50mA @ 5.5V. The current is drawn through the VTG line. The target should thus be able to supply at least this amount of power in addition to the requirements of the target board itself to avoid problems.

You have programmed the Lock Bits in a way that denies all write accesses to the FLASH and EEPROM memory, therefore you have to perform a complete chip-erase in order to re-program your AVR again.

If none of the above suggestions solves the issue, then you should consider the hardware design of your ISP interface. Please click here for more information on how to design the ISP interface.

You should also have in mind that ISP programming is dependent on the system clock. If using an external clock source, make sure the external clock circuit is designed correct.

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