35.3.1.2.1 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 \times 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 m s \times 12 b i t s \approx 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 35-3.

Table 35-3. Recommended BREAK Character Duration
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