AVR16EB32 datasheet(15/46 Pages) MICROCHIP

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AVR16EB32 Curiosity Nano

On-Board Debugger

User Guide

DS50003605B - 15

• Stop bits: One or two bits are supported.

3.4.4

Signaling

During USB enumeration, the host OS will start both the communication and data pipes of the CDC

interface. At this point, it is possible to set and read back the baud rate and other UART parameters

of the CDC, but data sending and receiving will not be enabled.

The terminal must assert the DTR signal when it connects to the host. As this is a virtual control

signal implemented on the USB interface, it is not physically present on the board. Asserting the

DTR signal from the host will indicate to the on-board debugger that a CDC session is active.

The debugger will enable its level shifters (if available) and start the CDC data send and receive

mechanisms.

Deasserting DTR in debugger firmware version 1.20 or earlier has the following behavior:

• Debugger UART receiver is disabled, and no further data will be transferred to the host computer

• Debugger UART transmitter will continue to send queued data ready for transfer, but no new

data is accepted from the host computer

• Level shifters (if available) are not disabled, and the debugger CDC TX line remains driven

Deasserting DTR in debugger firmware version 1.21 or later has the following behavior:

• Debugger UART receiver is disabled, and no further data will be transferred to the host computer

• Debugger UART transmitter will continue to send queued data ready for transfer, but no new

data is accepted from the host computer

• Once the ongoing transmission is complete, level shifters (if available) are disabled, and the

debugger CDC TX line will become high-impedance

Remember: Set up the terminal emulator to assert the DTR signal. Without the

signal, the on-board debugger will not send or receive data through its UART.

Tip: The on-board debugger’s CDC TX pin will not be driven until the CDC

interface is enabled by the host computer. Also, there are no external pull-up

resistors on the CDC lines connecting the debugger and the target, meaning the

lines are floating during power-up. The target device may enable the internal pull-

up resistor on the pin connected to the debugger’s CDC TX pin to avoid glitches

resulting in unpredictable behavior like framing errors.

3.4.5

Advanced Use

CDC Override Mode

In ordinary operation, the on-board debugger is a true UART bridge between the host and the

device. However, in certain use cases, the on-board debugger can override the basic Operating

mode and use the CDC TX and RX pins for other purposes.

Dropping a text file into the on-board debugger’s mass storage drive can be used to send characters

out of the debugger’s CDC TX pin. The filename and extension are trivial, but the text file will start

with the characters:

CMD:SEND_UART=

Debugger firmware version 1.20 or earlier has the following limitations:

• The maximum message length is 50 characters – all remaining data in the frame are ignored

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