When receiving data from the target, the on-board debugger will queue up the incoming bytes into 64-byte frames,
which are sent to the USB queue for transmission to the host when they are full. Incomplete frames are also pushed
to the USB queue at approximately 100 ms intervals, triggered by USB start-of-frame tokens. Up to 8 x 64-byte
frames can be active at any time.
If the host, or the software running on it, fails to receive data fast enough, an overrun will occur. When this happens,
the last-filled buffer frame will be recycled instead of being sent to the USB queue, and a full frame of data will be
lost. To prevent this occurrence, the user must ensure that the CDC data pipe is being read continuously, or the
incoming data rate must be reduced.
3.1.2
Mass Storage Disk
A simple way to program the target device is through drag and drop with
.hex
files.
3.1.2.1
Mass Storage Device
The on-board debugger implements a highly optimized variant of the FAT12 file system that has a number of
limitations, partly due to the nature of FAT12 itself and optimizations made to fulfill its purpose for its embedded
application.
The CURIOSITY drive is USB Chapter 9-compliant as a mass storage device but does not, in any way, fulfill the
expectations of a general purpose mass storage device. This behavior is intentional.
The on-board debugger enumerates as a Curiosity Nano USB device that can be found in the disk drives section of
the Windows device manager. The CURIOSITY drive appears in the file manager and claims the next available drive
letter in the system.
The CURIOSITY drive contains approximately one MB of free space. This does not reflect the size of the target
device’s Flash in any way. When programming a
.hex
file, the binary data are encoded in ASCII with metadata
providing a large overhead, so one MB is a trivially chosen value for disk size.
It is not possible to format the CURIOSITY drive. When programming a file to the target, the filename may appear in
the disk directory listing. This is merely the operating system’s view of the directory, which in reality has not been
updated. It is not possible to read out the file contents. Removing and replugging the kit will return the file system to
its original state, but the target will still contain the application that has been previously programmed.
To erase the target device, copy a text file starting with “
CMD:ERASE
” onto the disk.
By default, the CURIOSITY drive contains several read-only files for generating icons as well as reporting status and
linking to further information:
•
AUTORUN.ICO
- icon file for the Microchip logo
•
AUTORUN.INF
- system file required for Windows Explorer to show the icon file
•
KIT-INFO.HTM
- redirect to the development board website
•
KIT-INFO.TXT
- a text file containing details about the kit firmware, name, serial number, and device
•
STATUS.TXT
- a text file containing the programming status of the board
Info:
STATUS.TXT
is dynamically updated by the on-board debugger, the contents may be cached by the
OS and therefore not reflect the correct status.
3.1.2.2
Configuration Words
Configuration Words (PIC
®
MCU Targets)
Configuration Word settings included in the project being programmed after program Flash is programmed. The
debugger will
not
mask out any bits in the Configuration Words when writing them, but since it uses Low-Voltage
Programming mode, it is unable to clear the LVP Configuration bit. If the incorrect clock source is selected, for
example, and the board does not boot, it is always possible to perform a bulk erase (always done before
programming) and restore the device to its default settings.
PIC18F47K42 Curiosity Nano
Curiosity Nano
©
2019 Microchip Technology Inc.
User Guide
DS50002899B-page 8
