Figure 3-1. External Clock Footprint
The mEDBG CPU clock frequency depends on the selected voltage, see the table below.
Table 3-2. CPU Clock vs. Voltage
Target voltage
mEDBG CPU clock
3.3V
8MHz
5.0V
16MHz
3.2
mEDBG Configuration
The operation of the mEDBG can be configured by writing registers in the mEDBG. No configuration is
required for default operation.
3.2.1
mEDBG Low Power Modes
There are two modes that enable the mEDBG to save power when connected to an external power
source.
EOF mode
, where the mEDBG is disabled. When enabled the ATmega32U4 will enter sleep mode if the
USB does not enumerate within 5 seconds of power-up. In this mode, the external clock is not available
to the target MCU.
LOWP mode
, where the mEDBG is set to run at 1MHz. Saving power while maintaining the USB
connection for the COM port. The external clock will be 1MHz.
Table 3-3. Low Power Modes Operation
Mode
External CLK
COM port
ISP/dW program
ISP/dW debug
EOF
disabled
disabled
disabled
disabled
LOWP
forced 1MHz
enabled
useless
useless
Factory settings
enabled
enabled
enabled
enabled
3.2.2
mEDBG Fuse Filter
The mEDBG does not initially allow users to program all fuses of the target device through Atmel Studio,
as a filter is implemented to protect certain fuses. The protected fuses are different for every product
using the mEDBG and are typically clock related fuses that could be set to invalid configurations.
The fuse protection can be disabled by writing the FUSE bit to 0.
ATmega168PB Xplained Mini
©
2017 Microchip Technology Inc.
User Guide
DS50002636A-page 12
