31.3.1.2.1 BREAK in One-Wire Mode

In One-Wire mode, the programmer/debugger and UPDI can be totally out of synch, requiring a worst-case length for the BREAK character to be sure that the UPDI can detect it. Assuming the slowest UPDI clock speed of 4 MHz (250 ns), the maximum length of the 8-bit SYNCH pattern value that can be contained in 16 bits is

65535×250⁢ ⁢⁢ns=16.4⁢ ms/byte⁢=16.4⁢ ms/8⁢ bits=2.05⁢ ms/bit.

This gives a worst-case BREAK frame duration of
2.05⁢ ms⁢×12⁢bits ≈24.6⁢ ms
for the slowest prescaler setting. When the prescaler setting is known, the time of the BREAK frame can be relaxed according to the values from Table 31-3.
Table 31-3. Recommended BREAK Character Duration
UPDICLKSEL[1:0]Recommended BREAK Character Duration
0x1 (16 MHz)6.15 ms
0x2 (8 MHz)12.30 ms
0x3 (4 MHz)24.60 ms