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Fuses in Atmega16 and atmega32


New Member
Dear friends. The fuse registers in atmega32 are confusing. I am fully conversant with Atmel 8051 microns. I am beginning to learn avr Atmega. I don’t want any boot sector in my atmega32. I want to operate my mega32 with internal oscillator 1 MHz, low bod voltage, disable serial programming. I have got a Lab tool48 universal parallel programmer. I will be programming through this. Could anybody help me the values of fuse registers. Can the fuse registers be changed once programmed. Thanks in advance. I don’t need boot sector

Nigel Goodwin

Super Moderator
Most Helpful Member
You're probably somewhat confused by the 'terminology'? - the 'fuse' name comes for the VERY, VERY early days of OTP programmable controllers, where you physically 'blew' fuse links inside to set the options. This was obviously a 'one time only' process as once blown they couldn't be restored.

But this crude system was soon replaced by reprogrammable options, orignally be UV erasure on suitable devices, then by electronic erase on EEPROM based devices (one of the first of which was the MicroChip 16C84), and then later by electronic erasure on FLASH based devices (a LOT of manufacturers also claimed their EEPROM devices were FLASH when they weren't).

So while they are still called 'fuses' they haven't been so for a long time, well before AVR processors even existed.

So no problem changing them, and as for the actual settings you need to download and read the datasheet, which will explain all the (probably many) options.


Active Member
It depeds what You want to have.
For all possible Options You can use a FuseCalculator.
Nearly all the Fuses can be Changed.
When using ISP Programming the Controller has to had an functioning clock source.

E.g. When fused the Controller to external Clock source, there must be one there, or the Controller is not further functional.
Another mistake for ISP Programming is to disable the Reset Pin.

An error I've searched a long time for fix, is to let the JTAG enabled - That takes a few Pins from the Controller they can't be otherwise used then.
At ATMEGA 16 and greater this Function is activated at delivery!

The Lock Fuses are only to set.
To clear them the Controller has to be deleted completly.
I think for private using it is not nessesary to set them - It is a secure feature for commercenal use.

At delivery the ATMEGA 16 Controller is set to:
Reset Pin enabled
Internal Oscillator at 1MHz
Brown Out reset disabled
SPI ( = ISP ) enabled
JTAG ( = In System debugging ) enabled!!!
Lock Fused disabled
Boot Loader disabled

When exact timing doesn't matter and 8MHz is fast enough, You can use the internal Clock source.
You can increase the accurance of the clock by using the OSCCAL Procedure ( Take a look into the Datasheet or AN: AVR053 ).
When exact Clock frequencies or higher frequencies than 8MHz is needed, You should use an extenal Crystal e.g. for high speed serial connetions or watches.

Be aware, there are differet types of ATMEGA 16 availible ATMEGA 16, ATMEGA 16L, ATMEGA 16A ( list not complete ) .
They differ in a few availible Hardware options, operational Voltage and maximum Clock speed.
ATMEGA 16A has an own Datasheet!

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