higher speed data transfers

I have 2 arduinos communicating at 115,200. What does it take to go higher?

In the '328 data sheet:

20.10 Examples of Baud Rate Setting
For standard crystal and resonator frequencies, the most commonly used baud rates for asynchronous
operation can be generated by using the UBRRn settings in Table . UBRRn values
which yield an actual baud rate differing less than 0.5% from the target baud rate, are bold in the
Table 20-6. Examples of UBRRn Settings for Commonly Used Oscillator Frequencies table.
Higher error ratings are acceptable, but the Receiver will have less noise resistance when
the error ratings are high, especially for large serial frames (see ”Asynchronous Operational
Range” on page 194). The error values are calculated using the following equation:

Error[%] = ( (BaudRate (Closest Match)/ BaudRate) - 1) * 100%

shows that for fosc = 16.0000MHz, there's a couple of setting that yield 0% error at high speeds:

U2Xn = 0 U2Xn = 1
UBRRn Error UBRRn Error
250K 3 0% 7 0%

How do I set U2Xn and UBRRn?


How do I set U2Xn and UBRRn?

If you're using the standard Serial object, you don't need to. Just pass 250000 for the baud rate.

125K, 500K, and 1M are also zero-error baud rates. I use 250K exclusively now and have never had any problems. When I have time I'm even going to replace the bootloader with a 250K version.

Whoa, compiled ok!
Will fix up my serial test cable & give it a shot later.