User manual

Atmel-ICE [USER GUIDE]
42330A-MCU-07/2014
35
Note
If the SPIEN fuse was NOT left programmed, Atmel Studio will not be able to complete this
operation, and high-voltage programming must be used.
● During a debug session, select the 'Disable debugWIRE and Close' menu option from the 'Debug' menu.
DebugWIRE will be temporarily disabled, and Atmel Studio will use SPI programming to unprogram the
DWEN fuse
Having the DWEN fuse programmed enables some parts of the clock system to be running in all sleep modes.
This will increase the power consumption of the AVR while in sleep modes. The DWEN Fuse should therefore
always be disabled when debugWIRE is not used.
When designing a target application PCB where debugWIRE will be used, the following considerations must be
made for correct operation:
● Pull-up resistors on the dW/(RESET) line must not be smaller (stronger) than 10kΩ. The pull-up resistor is
not required for debugWIRE functionality, since the debugger tool provides this
● Connecting the RESET pin directly to VCC will cause the debugWIRE interface to fail, and may result in
hardware damage to the Atmel-ICE
● Any stabilising capacitor connected to the RESET pin must be disconnected when using debugWIRE,
since they will interfere with correct operation of the interface
● All external reset sources or other active drivers on the RESET line must be disconnected, since they may
interfere with the correct operation of the interface
Never program the lock-bits on the target device. The debugWIRE interface requires that lock-bits are cleared
in order to function correctly.
9.3 Atmel AVR UC3 OCD
JTAG interface
On some Atmel 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 synchronised 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 8kHz. 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 stabilising 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 pullup (10kΩ 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. The Atmel-ICE does
not support the Shutdown sleep mode were this regulator is shut off. In other words this sleep mode cannot be
used during debugging. If it is a requirement to use this sleep mode during debugging, use an Atmel AVR ONE!
debugger instead.
9.4 SAM / Coresight OCD
Some SAM devices include an ERASE pin which is asserted to perform a complete chip erase and unlock
devices on which the security bit is set. This pin is NOT routed to any debug header, and thus the Atmel-ICE is
unable to unlock a device. In such cases the user should perform the erase before starting a debug session.
JTAG interface
The RESET line should always be connected so that the Atmel-ICE can enable the JTAG interface.