Tinyavr , Megaavr , And Xmega Devices - Microchip Technology Atmel-ICE User Manual

4.3.6 Special Considerations
JTAG Interface
On some Microchip AVR UC3 devices the JTAG port is not enabled by default. When using these devices, it is
essential to connect the RESET line so that the Atmel-ICE can enable the JTAG interface.
aWire Interface
The baud rate of aWire communications depends upon the frequency of the system clock, since data must be
synchronized between these two domains. The Atmel-ICE will automatically detect that the system clock has been
lowered, and re-calibrate its baud rate accordingly. The automatic calibration only works down to a system clock
frequency of 8 kHz. Switching to a lower system clock during a debug session may cause contact with the target to
be lost.
If required, the aWire baud rate can be restricted by setting the aWire clock parameter. Automatic detection will still
work, but a ceiling value will be imposed on the results.
Any stabilizing capacitor connected to the RESET pin must be disconnected when using aWire since it will interfere
with correct operation of the interface. A weak external pull-up (10 kΩ or higher) on this line is recommended.
Shutdown Sleep Mode
Some AVR UC3 devices have an internal regulator that can be used in 3.3V supply mode with 1.8V regulated I/O
lines. This means that the internal regulator powers both the core and most of the I/O. Only Microchip AVR ONE!
debugger supports debugging while using sleep modes where this regulator is shut off.
4.3.7 EVTI/EVTO Usage
The EVTI and EVTO pins are not accessible on the Atmel-ICE. However, they can still be used in conjunction with
other external equipment.
EVTI can be used for the following purposes:
• The target can be forced to stop execution in response to an external event. If the Event In Control (EIC) bits in
the DC register are written to 0b01, a high-to-low transition on the EVTI pin will generate a breakpoint condition.
EVTI must remain low for one CPU clock cycle to ensure that a breakpoint is triggered. The External Breakpoint
(EXB) bit in DS is set when this occurs.
• Generating trace synchronization messages. Not used by the Atmel-ICE.
EVTO can be used for the following purposes:
• Indicating that the CPU has entered Debug mode. Setting the EOS bits in DC to 0b01 causes the EVTO pin to
be pulled low for one CPU clock cycle when the target device enters Debug mode. This signal can be used as a
trigger source for an external oscilloscope.
• Indicating that the CPU has reached a breakpoint or watchpoint. By setting the EOC bit in a corresponding
Breakpoint/Watchpoint Control register, the breakpoint or watchpoint status is indicated on the EVTO pin. The
EOS bits in DC must be set to 0b10 to enable this feature. The EVTO pin can then be connected to an external
oscilloscope to examine watchpoint timing.
• Generating trace timing signals. Not used by the Atmel-ICE.
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4.4 tinyAVR , megaAVR
The AVR devices feature various programming and debugging interfaces. Check the device data sheet for supported
interfaces of that device.
• Some tinyAVR
do not have on-chip debug capability at all.
• Some tinyAVR devices and some megaAVR devices have the debugWIRE interface, which connects to an on-
chip debug system known as tinyOCD. All devices with debugWIRE also have the SPI interface for in-system
programming.
©
2020 Microchip Technology Inc.
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, and XMEGA
®
devices have a TPI interface. TPI can be used for programming the device only. These devices
Programmers and Debuggers
®
Devices
User Guide
On-Chip Debugging
DS50002999A-page 30