# Can an ATmega or ATtiny device signature be read while running?

While programming an ATtiny or ATmega, avrdude prints the device signature, in this example it is an ATtiny.

avrdude: Device signature = 0x1e910a


Can I read this signature on a running device using C++ code (avr-gcc)? For ATmega1280 there is a chapter 29.6.10 writing about it, but I'm a bit puzzled by how I can code it in C++.

I want to be able to make the device send its device ID back to the controlling PC, so the PC can make decisions on it.

You can use these macros that get defined automatically when you include <avr/io.h>:

SIGNATURE_0
SIGNATURE_1
SIGNATURE_2


For ATmega1280, they're defined as:

/* Signature */
#define SIGNATURE_0 0x1E
#define SIGNATURE_1 0x97
#define SIGNATURE_2 0x03


in iom1280.h (which is automatically included through <avr/io.h> when you compile code for the m1280)

For example, this will send the three bytes via UART:

uart_putc(SIGNATURE_0)
uart_putc(SIGNATURE_1)
uart_putc(SIGNATURE_2)


If you truly want to read the fuses, you'd need to use boot_signature_byte_get macro from <avr/boot.h>

• I used boot_signature_byte_get( 0x00 ), boot_signature_byte_get( 0x02 ), boot_signature_byte_get( 0x04 ) – jippie May 12 '12 at 12:42