37.3.1.2.1 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×12bits ≈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 37-3.
| UPDICLKSEL[1:0] | Recommended BREAK Character Duration |
|---|---|
0x0 (32 MHz) | 3.075 ms |
0x1 (16 MHz) | 6.15 ms |
0x2 (8 MHz) | 12.30 ms |
0x3 (4 MHz) | 24.60 ms |