Atmega fusebit doctor (HVPP+HVSP) – fix the fusebits

mega_fusebit_doctor_1Atmega fusebit doctor, as name says it, device for repairing dead Atmega (and Attiny from v2.04) family AVRs by writing correct fusebits. Most common mistakes or problems are a wrong clock source (CKSEL fusebits), disabled SPI programming (SPIEN fuse) or disabled reset pin (RSTDISBL fuse). This simple and cheap circuit will fix you uC in a fraction of a second. If in first case we can help ourself with clock generator, then in 2nd and 3rd cases bring uC back to life is impossible with standard serial programmer. Most of people do not decide to build parallel programmer because its inconvenient and its cheaper and faster to buy new uC.

High voltage programming

mega_fusebit_doctor_3This circuit uses the parallel and serial high-voltage programming method. With those methods, we can talk to our “dead” chips which have reset or isp disabled:
HVPP = high voltage parallel programming.
HVSP = high voltage serial programming.

Supported chips list:
Code to this point supports 145 chips, but not all have been tested. Tested are lighted green. Report a problem – and i make a fix :)
AT90s1200, Attiny11, Attiny12, Attiny13/A, Attiny15
Attiny2313/A, Attiny24/A, Attiny26, Attiny261/A, Attiny28, AT90s2333, Attiny22, Attiny25, AT90s2313, AT90s2323, AT90s2343
Atmega48/A, Atmega48P/PA, Attiny461/A, Attiny43U, Attiny4313, Attiny44/A, Attiny48, AT90s4433, AT90s4414, AT90s4434, Attiny45
Atmega8515, Atmega8535, Atmega8/A, Atmega88/A, Atmega88P/PA, AT90pwm1, AT90pwm2, AT90pwm2B, AT90pwm3, AT90pwm3B, AT90pwm81, AT90usb82, Attiny84, Attiny85, Attiny861/A, Attiny87, Attiny88, AT90s8515, AT90s8535
Atmega16/A, Atmega16U2, Atmega16U4, Atmega16M1, Atmega161, Atmega162, Atmega163, Atmega164A, Atmega164P/PA, Atmega165A/P/PA, Atmega168/A, Atmega168P/PA, Atmega169A/PA, Attiny167, AT90pwm216, AT90pwm316, AT90usb162
Atmega32/A, Atmega32C1, Atmega323/A, Atmega32U2, Atmega32U4, Atmega32U6, Atmega32M1, Atmega324A, Atmega324P, Atmega324PA, Atmega325, Atmega3250, Atmega325A/PA, Atmega3250A/PA, Atmega328, Atmega328P, Atmega329, Atmega3290, Atmega329A/PA, Atmega3290A/PA, AT90can32
Atmega64/A, Atmega64C1, Atmega64M1, Atmega649, Atmega6490, Atmega649A/P, Atmega6490A/P, Atmega640, Atmega644/A, Atmega644P/PA, Atmega645, Atmega645A/P, Atmega6450, Atmega6450A/P, AT90usb646, AT90usb647, AT90can64
Atmega103, Atmega128/A, Atmega1280, Atmega1281, Atmega1284, Atmega1284P, AT90usb1286, AT90usb1287, AT90can128
Atmega2560, Atmega2561


mega_doctor_renderJust put your dead mega in socket, press the START button, and enjoy your good-as-new processor. There are three slots on board, for most common AVR’s, pins compatible with: Atmega8, Atmega16, Attiny2313. There is also an extra goldpin connector with all signals so you can attach adapters:
#1 adapter” as HVPP extension, for 20pin Attiny26 compatible and 40pin Atmega8515 compatible processors.
HVSP adapter” for 8pin and 14pin HVSP processors.
Or make your own adapters for other types of processors, in trough-hole or surface-mounted, you can use the breadboard for this – just connect signals to correct pins. How? Check your AVR datasheet, go to “memory programming” and then “parallel programming” – check the signal names, all signals are described under the DIP40 slot. In doctor memory there is a lot of free space so project may be developed all the time. One sided PCB with 55mm x 92mm dimensions. On top side you need to solder several jumpers, or, make this PCB as double sided – choose yourself. Resistors from R7 to R23 may be in 100ohm to 10K, but i suggest from 470ohm to 1K.

While mounting the DIP40 slot, you must to remove it pins from 29 to 37. These pins must not have electrical contact with inserted uC pins, traces runs there only to make the board smaller (onesided). Take a look at pic on the left, these you must remove from slot.


fusebit_doctor_adapters_4The ALLOW ERASE jumper allows doctor to erase whole flash and eeprom memory, if it is open, doctor will newer erase memory but may not cure device if lockbits are enabled, so you choose. After insert dead uC and press the START button, doctor will initiate the parallel or serial high-voltage programming mode. This is chosen automatically, device will recognize HVSP adapter and start to work in HVSP mode. After that, doctor wait for high state at RDY/BSY line. Then, read device signature and check if it supports it. Next, memory erase is performed if user allows that. Then lockbits are checked, and if they not blocking device, doctor sets all fusebits to fabric, having regard to whether there are extended fusebits or not. Some of older AVR have only one byte of fuses – LOW – and this is also included. After fusebits are verified, the proper leds is flashed.

Leds explanation:

green on – patient successfully cured, fusebits repaired. If lockbits are enabled, just verify fusebits with factory ones – and if they ok – light up green.
red on – signature problem, can’t read, no device in socket, or no such signature in database.
green flashing – signature ok, fusebits are wrong. Lockbits enabled, chip erase permission required (read below).
red flashing – signature ok, no lockbits, but for some reason can’t write new fusebits.


Note that terminal is not needed, device works without pc, and all we want to know we get from leds.
You can find extra RS232 output, and connecting this to the terminal, sends all information about fixing process – see exemplary printscreens in gallery. All the info is send “on fly” via uart. Use proper converter to connect this with pc. If you have COM port for RS232, use MAX232 based converter (eg this). If you are using laptop, use the USB converter (like this or this).

Terminal settings:
baudrate: 4800
parity: none
databits: 8
stopbits: 1
handshake: none


prototype_docUse one of the following microcontrollers as the doctor-chip: Atmega8, Atmega88, Atmega88P, Atmega168, Atmega168P, Atmega328, Atmega328P – and their newer/low-voltage “A” or “L” versions.
Use stabilized 12V supply voltage. Higher voltage can damage fixed chip!

Code was written based on high-voltage parallel and serial programming section of datasheet of suitable AVRs.
If you are searching for attiny family AVR’s fusebits fix device, then check my previous project, the Attiny fusebit doctor. Unfortunately, some bugs show off and this project is no longer updated since the “Atmega fusebit doctor” supports all the Attiny family AVRs. But, source code is attached for this project, and with avr datasheet, it will be easy to understand this programming mechanism.


Internal 1MHz clock, and enabled EESAVE bit – see README file.
If you use a brand new chips as doctor, you don’t need to change anything – 1MHz clock is already set as default. EESAVE bit is optional. It disallows to erase the eeprom when firmware is actualized, eeprom is used to store the fixed chips counter which is send trough uart.


Send your own fuses and locks trough terminal, talk with chips with broken signature. If you connect terminal Tx pin to PCB Rx pin – manual mode will be enabled automatically. This requires Tx-terminal pin to be HIGH and OUTPUT when idle. It must pull up the 10K pulldown. If this condition is not met, doctor will work in normal – automatic mode.

First, doctor will read signature. And if fail, it will ask to type signature manually.
Type two last bytes of signature in HEX (4 chars) and hit enter.

Then, doctor will try to read the chip depending on given signature.
When succeed, select an option:
1 – write fusebits – this will perform a fuse write cycle with fuse-values from buffer (default).
2 – modify fusebits – this will let you to type fuses manually, values in buffer will update. Type one byte in HEX (2 chars) and hit enter. Repeat for each byte (if exist).
3 – set lockbits – type new lock value in HEX (2 chars) and hit enter – do this with caution! Remember that unused bits are always 1! E.g. if want to enable LB1 and LB2, type FC (11111100)
4 – erase the chip – this will just erase the chip and locks, it require “allow erase” jumper for safety.
5 – end – exit programming and drop voltages, now you can safely remove the chip.

See how Attiny13 with broken signature was repaired.
See how the same chip was “broken” again.
Do not suggest LEDs when in manual mode – they just blinking randomly :)
ATTENTION – Firmware 2.1x NEED a pcb updated to version 2h!



DOWNLOAD – ARCHIVE of all previous updates. Firmwares + boards.
Changelog in README file. -SMD VERSION HERE-
No need to download this, all newest files are below.

DOWNLOAD – UPDATE #11, 30.04.2011:
Firmware ver.2.11 – fixes
Fusebits: see README file

Fixed bug when not writing the HIGH fusebyte (concerns all chips!)
“Just” a typo which i made during optimalisations for 2.10 firmware :)

Pads for 4 chips, compatible with: T2313, M8, M16, M128 – all has been tested.
Use strong paper clips to push chip to the pads.

FAQ – frequently asked Questions and Answers: (update 2014-02-01)

Q: No sign of life, no leds are working.
A: Critical bugs on pcb, poorly programmed chip.

Q: Red led is on.
A: Chip si not recognized. Make a voltage measurements. In idle, measure voltages on +12 RESET and +5 SUPPLY at female goldpin connector – you should get 0V or close to 0V on both. After the START button is pressed, you should get close to +12V and 5V for one second. If not, check transistors, if they are ok and if they are soldered ok.

Q: Red led is on.
A: Bugs on pcb, traces are packed densely and its very possible that you have invisible gap, shortcut, or dry joint. Check everything with multimeter, but PRECISELY.

Q: Red led is on.
A: Connect device to the terminal to get repair log. Press start to receive infos.

Q: Received “Init programming…” and nothing more – OR – received signature is “00 01 02” or “FF FF FF”.
A: Chip is broken, or there still are bugs on pcb – look above.

Q: Received signature is “1E 90 00″, ” 1E 1E 1E”, or something familiar (meaningful data).
A: Chip is good, it initiates, look for shortcuts on DATA, BS, XA lines.

Q: Green led is on / “Verifying… – OK!” received, but chips don’t work with standard programmer.
A: You can be 100% sure that fuses are fixes, chip have hardware ISP damaged or it have some other damage.

Q: What are “Read Signature… FAIL!” and “Trying T2313 pinout… OK” doing in log?
A: Alle the 20pin chips need to be threated individually. First, device tries to read chip with standard schematic, and if it fails (“FAIL!”), then it tries to use schematic for 20pin T2313 compatible chips and then chip is read properly. This is normal behavior, this not a bug.

Q: What are “<[2J" trashes doing in log? A: This is a terminal clear screen sequence, turn on the “VT-100” emulation in terminal settings.

Q: I’m trying to type data into terminal but no chars appearing.
A:Make sure you set handshake to NONE in terminal settings.

Q: After typing data into the terminal, i can’t confirm them with return key and can’t type next ones.
A: When pressing return, your terminal must have to send the CRLF chars, if not, check your settings.

Q: This still doesn’t help me, i tried everything but still have the problem.
A: Ask in comments below :) Post firmware version and pcb version with which you try to work, paste the repair log.

Q: Do all these 1K series resistors (R7 up to R23) are really needed here?
A: No, you can build the circuit without them. But remember, if for some reason out patient will not enter in the programming mode and continue with its code, then logic state conflict will occur between two microcontrollers which can damage them permanently. These resistors are to protect the circuit against such situations. I strongly recommend to build it exactly as schematic says.

Q: Pulldown resistors for 12V and 5V lines (R24 and R27) are heating up quite strongly in manual mode, and whole circuit takes more power, can i change them for something higher value?
A: Yes, but circuit can work incorrectly with some of the patients. When idle, voltages should be near 0V, and when powering on or off, their edges should have proper steepness to provide good timing (see entering high voltage programming in datasheet). Because only simple bipolar transistors are used, these resistor guarantee above requirements. The interesting case is an attiny2313 problem when all the fuses were correctly burned, without one, the RSTDISBL. As it showed up, because of bad edges of 12V reset voltage, this uC although was working in parallel mode, but not in high voltage, so it was not allowing to change that fuse – this is my own interpretation so i can be wrong.

Q: My chip is read properly but doctor can not write new fuses, allow erase is enabled.
A: If the ISP programmer acts the same way, then your chip is damaged, nothing can do.

Q: Without a patient, circuit acts awkward, it freezes, and goes on when i put my finger near the traces.
A: This circuit is not meant to be used without a patient. It acts in such way because when entering in programming mode, it is waiting for a high state on the RDY pin from patient. This pin is not pulled down and works as high impedance input, so electrostatic charge from your finger is read as high state and code goes on further.

Q: Chip names are not appearing in the log, i see “no names in 8kB ver” instead.
A: Chip names are not displayed in 8kB versions of the firmware, i.e. for atmega8 and atmega88 – because names don’t fit in such memory space. If you want the names, use atmega168 or atmega328 chip and burn proper firmware.

ALWAYS use the newest version of the firmware. Hex and bin files are the flash memory files, use one of them. No need to program eeprom memory.

Русский перевод – Евгений из GetChip Блог.

3.00 avg. rating (71% score) - 2 votes


  1. I disabled the reset function on the tiny85 to use it as digital pin and later I tried to reset it but it’s stuck on “Init programming”. It’s odd because I can restore mega328p chips. Also I was able to restore this attiny85 using this
    Whats could be the problem?

    • Check quality of your +12V reset and +5V supply voltages slopes at rise and fall. If they are bad (timing is bad, rise or fall is long, it shows some riplle) then the patient chip can be in normal programming mode, not HV.

      This was the issue with T2313. If slopes was low quality or timing was bad, T2313 entered parallel programming but not HV, and function of the reset line could not be changed. Also there was no communication after disabling reset.

      Did you change pull down resistors for +12V and +5V lines?

      And last question, it is in HVSP mode?

  2. Thanks for your answer. I was in HVPP mode with the ATtiny85 connected. I watched your video again and noticed it enters HVSP mode with the tiny adapter connected. This made me realize I had missed something when I was designing my adapter. I hadn’t connect the XTAL1 and OE pins. I will add a jumper on the main board for them. It fixed my ATtiny85 after connecting these two pins.

    Watching your video again I saw that your board prints on serial monitor:
    “No chip in socket…
    Thank you”
    even without a chip or an adapter connected.
    Mine is stuck on “Init Programming” if I don’t have a chip connected. Is this normal? Could I have missed anything else? If connect a chip I don’t have any problem.

  3. Hello again,
    I build a new fusebit doctor without sockets on the main board. It works only with adapters. I used a boost converter module from ebay to convert 5V to 12V. That way it works with only 5V power supply or a power bank.
    It works fine with atmega328p chips but I’m stuck again with the attiny85. I tried 5 of them (2xDIP and 3xSMD). It reads the device signature successfully of only one of them. On the other four I am getting something like:
    Read signature… 00 00 00 – FAIL!
    Read signature… FF FF FF – FAIL!
    or something random like:
    Read signature… 0E FF 90 – FAIL!
    Read signature… 3F 3F 37 – FAIL!
    These 4 chips work fine and I’m able to read the fuses and flash them using a usb programmer. What should I look for on my new board? I used smd components(uC, resistors, transistors) and the only thing I changed is the R6 value from 4K7 to 1K, because I was getting 4.6V on the 5V rail. With the 1K I get 4.8V.

  4. Cześć,

    Uruchomiłem urządzenie wg Twojego projektu – zadziałało bez problemów za pierwszym razem. Naprawiłem posiadane wszystkie 3 nie dające się programować ATmegi 8 – wszystkie ożyły.

    Świetny projekt – serdeczne podziękowania za Twoją prace i gratulacje za skuteczny i dopracowany projekt.

  5. Hello! Help me please.
    I locked chip AT90pwm3b. I made your doctor chip. Restored LB and ExB.. H-byt not restored(HB=00 )! What could be the reason?

  6. Add that the signature is read correctly, the freezing of the chip was as follows: LockByte=00, LowByte=2c, HighByte=21, ExtByte=06
    After processing: lock= FF Low =62 High=00 Ext=1F
    chip erase I’ve made.

    • Hello, default fuses for AT90pwm1/2b/3b should be L=62, H=DF, E=F9.

      Can you paste here terminal log?

      Can you check your board with some other AVR chip?

      And you do not need this device to unlock lockbyte. You do this in your regular programmer by doing erase chip command.

  7. Hello! I tested my board on chip mega8. I found that= I can write any which want a low bytes. But I can not change High bytes

  8. programming… DONE
    Read signature… 1E 93 07
    Searching chip… no names in 8kB ver
    Read fusebits… L:FF H:DF E:00
    Should be… L:E1 H:D9 E:00
    Lockbits… DISABLED (FF)

    What to do?…
    1 – write fusebits
    2 – modify fusebits
    3 – set lockbits
    4 – chip erase
    5 – end

    Type fuse LOW: e1
    Type fuse HIGH: d9
    Writing E1 D9 00… DONE
    Verifying… L:E1 H:DF E:00- FAIL!
    Please try again…

  9. I made connect AT90pwm3b/ result-I can load any value Low and Ext bytes! HighByte is not loaded.
    this writen HyperTerminal

  10. YES!!! THANK YOU!!! I regained the chip !! :)
    version 2.11 !!!!!!

  11. >>But, source code is attached for this project
    BTW, where i can find source code?

  12. Why you closed source code of atmega doctor? This is a great project, but why you isolate the source code from community help and debugging?…

  13. Init programming… DONE
    Read signature… 00 00 00 – FAIL!
    Type the signature: 1E
    Can not lock atmega8-16PU

  14. Can this device lock, if I puted RSTDISBL bit?

  15. Hi can anyone point me out please?

    Cant get signature read red led tuns off then green flashes few times and Red comes back again :(

    if i do termianl it fails to verify after flash and i have to tell signature manualy


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