AVR HVSP Fuse Resetter





Introduction: AVR HVSP Fuse Resetter


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

Example Operation

Step 1: Design Notes

design notes

to minimise 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 thru device name and various fuse values in hexidecimal 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.

Step 2: Parts List

parts list

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

project fuse setting

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

Step 3: Operation


* place 8 pin target device on breadboard
* for 14 pin targets, jumper wire to breadboard
* apply 12V power
* display shows device name upon identification
* press and release button to cycle display content
* displays device name, fuse hi bits, fuse low bits and fuse extended bits
* long press and release button to reset fuse to factory default

Step 4: Breadboard Layout and Schematic

[2017-12-21] Rick sent me a correct schematic for the project, where he points out that R. Schenk's schematic has pin
8 of the DUT connected to Vcc but it should be connected to pin 18 of the 2313 (anode 1). Rick was kind enough to provide a corrected schematic (below)

[2016-11-29] I had replace the schematic w/ a correct one done by a builder R. Schenk. Thanks R. (error in this schematic, removed)

* some components shown above are restricted by drawing software (fritzing), see actual photo, the physical layout fits a lot nicer
* the two green pins are to be connected to a 12V power source. i use an A23 12V battery but i can only find a 2xA23 battery holder. you may use whatever is available to you.
* the six red pins are approximate locations for an ISP programmer hookup, you will need to connect the 2nd pin (from left) to pin 1 (RESET, blue wire) of the tiny2313 during programming. in-circuit programming is a hit and miss, as our programming pins are connected to many devices. for the least, you need to remove the led module before attempting to program isp fashion. if fails, you need to remove 2313 and have it programmed off circuit.

Step 5: Assembly

* follow breadboard layout
* place 2313 first, then layout wires
* i use ethernet cat-5 wires, more than one wire can share a single tie-point
* layout tactile button, transistor, voltage regulator and two resistors as directed
* the 4x7 segment led module goes in last, on one side the pins shares the same tie-points that the 2313 also occupies
* since most io pins are share-purposed, you will have trouble programming the 2313 in circuit. i would program it off circuit and put it back on the breadboard

Step 6: Source Code

click to download fuse.c
click to download makefile

i am not detailing the development enviroment here. my setup is avr-gcc under linux. if you have trouble you can also use the following hex files and skip the build

click to download fuse.hex
click to download fuse.ee.hex



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    Hi there,

    Did the wiring based on the source code and also changed the hex assignment of the characters since I'm using common cathode 4x7 segment LED instead of common anode as per suggestion but still can't get it right. In fact, I'm actually wondering how does assigning SEG_D_PD to _BV(7) actually maps it to PA1 in the attiny? This is also true for SEG_d_PD_BV(6) as per definitions. Is there anything else I need to change in the code to match the operation to a common cathode 4x7 seg LED? Looking forward to your insight, thanks!

    I have unlearned AVR for more than 4 years so I may not be able to help on this old project.

    For SEG_D_PD and SEG_d_PD, the comments d.7 maps a.1 and d.6 maps a.0. This is virtual mapping. As shown in the schematic, PORTD 6 and 7 are not connected to the LED module, instead it is PORTA 0 and 1 that connects to segment D and decimal point. I used virtual mapping to simplify the logic and save space. You can see later in the code the porta values are from portd variable....

    uint8_t porta = portd >> 6;

    portd &= 0x3f;

    It should be enough to just comment / uncomment this line

    //#define _REVERSE

    to change CC or CA led modules.

    If you are still not getting anywhere, try and comment out blocks of code until just the display left and see if it can show. You can also write very simple blinky program just to turn on one digit / segment at a time to debug.

    Hi there :)

    Thanks for the quick response! Your explanation about the mapping was very helpful to understand by the code. Also, I tried commenting #define _REVERSE with having the same setup for the characters for common cathode LED but to no avail. I'm only getting the first digit all lit up and pushing the button doesn't light up anything. Pushing it long to reset gives a dash at the last digit. I guess it must be the display problem. Haven't tried commenting other blocks but will try to understand first how to display in LED by debugging it through Blinky. Thanks a lot for your help!

    Did you set the fuse accordingly? Looks like the multiplexing is not working. It is done by the timer interrupt and since we are not using crystal, the fuse must be set to use internal oscillator (if I remember correctly).

    Yes I set the fuse as per instruction. In that case, I might have to learn how to fix the multiplexing in the code :)

    it is very useful product. what can i do for you. If you need I can provide you with the 7 segment LED digital display. because we are 7 segment LED digital display manufacturer,Wuxi ARK Technology Electronic co.,Ltd. in China .My name is Judy.email :wangql@arkch.com


    Can I combine the VUSBTiny project with this?
    Also, I want to omit the LED display and show the needed data via serial (vusb)
    Is this possible?

    Thank you.

    sorry, I meant Good project.

    God project.
    Use it to reset ATTINY85 in vusbtiny project.
    Left the LED portion out I was not able to get the same LED display with same pinout.
    Just insert target and do a long press, remove target and check ATTINY85 with programmer.


    If is common cathode how to change, I am a noob in avr.