UPDI Enable

The dedicated UPDI pad is configured as an input with a pull-up.

When the pull-up is detected, the debugger initiates the enable sequence by driving the line low for a duration of t_Deb0, as shown in Figure 37-5:

Figure 37-5. UPDI Enable Sequence

Table 37-4. Timing in the Figure
Timing Label	Max.	Min.
t_RES	200 µs	10 µs
t_UPDI	200 µs	10 µs
t_Deb0	1 µs	200 ns
t_DebZ	14 ms	200 µs

When the negative edge is detected, the UPDI clock starts. The UPDI will continue to drive the line low until the clock is stable and ready for the UPDI to use. The duration of t_UPDI will vary, depending on the status of the oscillator when the UPDI is enabled. After this duration, the data line will be released by the UPDI and pulled high.

When the debugger detects that the line is high, the initial SYNCH character 0x55 must be transmitted to synchronize the UPDI communication data rate. If the Start bit of the SYNCH character is not sent within maximum t_DebZ, the UPDI will disable itself, and the UPDI enabling sequence must be reinitiated. If the timing is violated, the UPDI is disabled to avoid unintentional enabling of the UPDI.

After a successful SYNCH character transmission, the first instruction frame can be transmitted.