On Linux machines, the CDC will enumerate and appear as
/dev/ttyACM#
.
On MAC machines, the CDC will enumerate and appear as
/dev/tty.usbmodem#
. Depending on
which terminal program is used, it will appear in the available list of modems as
usbmodem#
.
Info:
On older Windows systems, a USB driver is required for CDC. This driver is included in
MPLAB X and Atmel
®
Studio installations.
3.1.1.2
Limitations
Not all UART features are implemented in the on-board debugger CDC. The constraints are outlined
here:
•
Baud rate
must be in the range 1200 bps to 500 kbps. Any baud rate outside this range will be set to
the closest limit, without warning. Baud rate can be changed on-the-fly.
•
Character format
: Only 8-bit characters are supported.
•
Parity
: Can be odd, even, or none.
•
Hardware flow control
: Not supported.
•
Stop bits
: One or two bits are supported.
3.1.1.3
Signaling
During USB enumeration, the host OS will start both 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.
When a terminal connects on the host, it must assert the DTR signal. This is a virtual control signal
implemented on the USB interface, but not in hardware in the on-board debugger. Asserting DTR from
the host will indicate to the on-board debugger that a CDC session is active, will enable its level shifters
(if available) and start the CDC data send and receive mechanisms.
Deasserting the DTR signal will not disable the level shifters but disable the receiver so no further data
will be streamed to the host. Data packets that are already queued up for sending to the target will
continue to be sent out, but no further data will be accepted.
Remember:
Enable to set up your terminal emulator to assert the DTR signal. Without it, the
on-board debugger will not send or receive any data through its UART.
3.1.1.4
Advanced Use
CDC Override Mode
In normal operation, the on-board debugger is a true UART bridge between the host and the device.
However, under certain use cases, the on-board debugger can override the basic operating mode and
use the CDC pins for other purposes.
Dropping a text file (with extension
.txt
) into the on-board debugger’s mass storage drive can be used
to send characters out of the CDC TX pin. The text file must start with the characters:
CMD:SEND_UART=
The maximum message length is 50 characters - all remaining data in the frame are ignored.
ATtiny1607 Curiosity Nano
Curiosity Nano
©
2019 Microchip Technology Inc.
User Guide
DS50002897A-page 7
