westfw:
You can't change Fosc just by changing code; you have to change the physical crystal/resonator attached to the chip.
18.432MHz would probably be a better choice, but you'd probably still need to change a lot of other Arduino code.With the usual 16MHz resonator, 57.6kbps should be THAT far off (about 2.1%, whereas async communications will normally allow a combined error of up to 5%.) WormFood AVR BRG calculator
Now, it turns out that the Ardunino code contains a hack that causes 57600bps to be LESS accurate than it could be, in the name of backward compatibility. If the normal bitrate isn't close enough, try using:
Serial.begin(57601);
57600 baud with a 16.0 crystal comes out very close:
[b]Enter crystal frequency: 16
Crystal frequency is 16.000000
Enter serial baud rate : 57600
F_CPU MHz : 16.000000
UBRR reg : 34 (0x0022)
UBRRH reg : 0 (0x00)
UBRRL reg : 34 (0x22)
U2X bit : SET
Baud : 57600
Actual : 57142.857
Pct error : -0.794%
[/b]