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Wednesday, April 6, 2011

hvsp fuse resetter - simpleavr

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hvsp fuse resetter

AVR ATTINY HVSP Fuse Resetter / Reader

Video Link...

hvsp fuse resetter probing a target tiny85 device


in working w/ 8 or 14 pin avr devices, i would sometimes want to use the RESET pin as io as the io pin count is low. but doing so will disable further programming via SPI. i do not need a full blown HV programmer, just a way to revert these devices to factory default fuse settings so that i can use SPI to flash them again. it is also handy as sometimes by mistake i may burn wrong fuse value and brick my devices.

this project is created so that if i could revert the RESET fuse change and flash via SPI again. it employs the high-voltage serial programming (hvsp) available for such devices. note that this is not to be confused w/ the high-voltage parallel programming used for 20pin+ devices (i.e. tiny2313, mega8, etc).


  • reads device signature and hi-low fuses for hi-voltage serial programmable attinys
  • reset hi-low fuses to factory default on target devices
  • layout to drop-on attiny13, attiny25/45/85 8 pin devices targets
  • attiny24/44/84 targets needs additional breadboard and jumper wires
  • standalone operations, fuses values show on 7 segment display
  • cannot reset fuse for attiny2313 and atmega devices as they requires hi-voltage parallel programming

design notes

to minimize project component count, the 4 digit led module is directly driven by the 2313's io pins. neither transistors nor current limiting resistors are used. for more detail implementation notes, please see my digital alarm clock project. the led driving takes up 12 io pins (4 digits + 7 segments + decimal point).

for hvsp purpose, we need to have 6 io pins from t 2313. we need to supply 5V Vcc, 12V to RESET, SCI (serial clock input), SII (serial instruction input), SDI (serial data input) and SDO (serial data out). for that we employ the rest of the free io pins from the 2313, plus some io pins are shared between led driving and hvsp control.

one single tactile button is used to accept input, this io pin is shared between button input and led driving.

upon attaching power firmware reads target mcu device signature via AVR's HVSP (High-Voltage Serial Programming) interface. it then look up the device name by matching the device signature. in turn, fuse values (hi, low and extended) are read from device.

fuse values can then be read by pressing the tactile button, which cycles threw device name and various fuse values in hexadecimal format.

pressing and holding the tactile button for about one second will instruct firmware to write the factory default fuse value to the target mcu device. after writing, firmware re-reads the new fuse values for display.

at all times a timer interrupt is used to perform led multiplexing. brightness can only be adjusted by source code change.

i had included the more common device types, source code is provided so that different / additional device can be added to the firmware. please note that only devices with HVSP support can be used.

the circuit requires a main power of 12V supply, a 78L05 voltage regulator brings a 5V Vcc for the 2313 to operate. a 2n2222 is used to switch on 12V towards the target device's RESET pin when HVSP read / writes are being commenced.

project fuse setting

avrdude -c usbtiny -p t2313 -V -U lfuse:w:0xe4:m -U hfuse:w:0xdf:m -U efuse:w:0xff:m

parts list

  • attiny2313
  • 4x7 segment LED display
  • 1k resistor x 2
  • 2n2222 NPN transistor or equivalent
  • 78L05
  • mini breadboard 170 tiepoints
  • +12V battery source



hvsp fuse resetter probing a target tiny85 device
AVR HVSP on a tiny breadboard - Hack a Day
hvsp fuse resetter - simpleavr
Make your own minimalist AVR ISP - Hack a Day
YouTube - AVR ATTINY HVSP Fuse Resetter / Reader

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