AT90S datasheet, AT90S circuit, AT90S data sheet: ATMEL – 8- Bit AVR Microcontroller with 4K Bytes of In-System Programmable Flash. AT90S datasheet, AT90S circuit, AT90S data sheet: ATMEL – 8- bit Microcontroller with 2K/4K bytes In-System Programmable Flash,alldatasheet . AT90S, datasheet for AT90S – 8-bit Microcontroller with 2K/4K bytes In- System Programmable Flash provided by ATMEL Corporation. AT90S pdf.

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Certain features of AVRs are controlled by fuse bits. For example, settings like clock options or the brown-out reset circuit are configured with these bits. So, for instance, to set the AVR to use an external oscillator, you must set this at the moment you program it. There is no way to change the clock behavior through the program code. If you change your mind, you must reprogram the AVR.

AT90LS datasheet & applicatoin notes – Datasheet Archive

The details of how to program the fuse bits in your AVR depend on the particular programmer you are using. Consult the manual about the details. A little oddity is that to program a feature, you must write a “0” to the particular wt90s4433.


It’s sort of a negative logic. If you are programming the fuse bits with AVR studio, you don’t have to worry about this issue because the ay90s4433 of the fuse bit is managed by the programmer.

AT90S4433 Datasheet PDF

Fuse bits live in a different memory space than the program memory. This means that the fuse bits are not affected by a program memory erasure. This has the advantage that once you program the correct fuse bits in your AVR, you can forget about them and don’t need to reprogram them each time you alter the program memory.

Fuse bits differ greatly between different AVR variants. I will explain the AT90S’s fuse bits. AVRs have two programming modes, parallel and serial. See the Memory Programming section of the datasheet for details. The default value for this fuse is programmed. You can change this fuse only datasehet you are programming the AVR in parallel mode.

The Brown-Out Detector circuit monitors the Vcc voltage. When Vcc drops below the trigger level, this circuit resets the AVR. When Vcc is above the trigger level, the reset signal is released. The following table summarizes this: There are several options for the AVR clock which differ in the start-up time after a reset.


You need to adjust the start-up time according to the clock source you are using.

See the datasheet and the clock section for more details. A common pitfall with fuses is to forget about them, so you end up working with the default settings. If you are lucky, these are the settings you need, but if you are not, strange things will happen.

For instance, many AVRs have an internal oscillator, which is enabled by default. If you are using the UART based on the frequency of an external oscillator, your serial link won’t work. Or maybe your Atmega is not working as expected, because you forget to unprogram the Atmega compatibility mode fuse, which is programmed by default.

So, here is my advice: Carefully check the fuse bits before using your AVR!