Microchip Technology megaAVR 0 Series Manual page 444

the BREAK character should be transmitted at the slowest recommended baud rate setting for the
selected UPDI clock according to
Table 29-3. Recommended BREAK Character Duration
UPDICLKSEL[1:0]
0x1 (16 MHz)
0x2 (8 MHz)
0x3 (4 MHz) - Default
29.3.2 Operation
The UPDI must be enabled before the UART communication can start.
29.3.2.1 UPDI Enable
The dedicated UPDI pad is configured as an input with pull-up.When the pull-up is detected by a
connected debugger, the UPDI enable sequence, as depicted below, is started.
Figure 29-5. UPDI Enable Sequence
1 Drive low from debugger to request UPDI clock
2 UPDI clock ready; Communication channel ready.
UPDIPAD
UPDI.rxd
UPDI.txd
debugger.
UPDI.txd
When the pull-up is detected, the debugger initiates the enable sequence by driving the line low for a
duration of T
Deb0
is done.
The negative edge is detected by the UPDI, which requests the UPDI clock. The UPDI will continue to
drive the line low until the clock is stable and ready for the UPDI to use. The duration of this T
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 sent to
properly enable the UPDI for communication. If the Start bit of the SYNCH character is not sent well
within maximum T
©
2018 Microchip Technology Inc.
Table 29-3:
1
Handshake / BREAK
T 10us
min
T 200us
max
(Ignore)
2
Hi-Z
UPDI.txd = 0
T 10us,
min
T 200us
max
Hi-Z
Debugger.txd = 0
T 200ns
min
T 1us
max
to ensure that the line is released from the debugger before the UPDI enable sequence
, the UPDI will disable itself, and the enable sequence must be repeated. This time
DebZ
Unified Program and Debug Interface (UPDI)
Recommended BREAK Character Duration
6.15 ms
12.30 ms
24.60 ms
St D0
Hi-Z
Debugger.txd = z.
T 200us,
min
T 14ms
max
Datasheet Preliminary
®
megaAVR 0-Series
D1 D2 D3 D4 D5 D6
SYNC (0x55)
(Autobaud)
Hi-Z
UPDI
DS40002015A-page 444
D7 Sp
will