34.3.1.2.1 BREAK in One-Wire Mode
In Asynchronous 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:
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 the next table:
| UPDICLKDIV[1:0] | Recommended BREAK Character Duration |
|---|---|
0x0 |
Reserved |
0x1 (16 MHz) |
6.15 ms |
0x2 (8 MHz) |
12.30 ms |
0x3 (4 MHz) - Default |
24.60 ms |