Board Description:

This board enables you to flash a custom board with a PIC-type microcontroller via a USB-C port. Recognized as a debug accessory, it can supply up to 500mA through the VBUS lines, making it ideal for flashing devices that adhere to the power delivery specification.

The resistors labeled R2 and R3 function as pull-up resistors, setting the voltage on the CC lines to enable the board’s detection as a debug accessory.

A 5V input (J1), safeguarded against overvoltage and reverse polarity, enables the external power supply to the board through a switch. When power is supplied, the LED illuminates.

When programming the board with MPLAB X IDE, ensure the USB-C cable is correctly oriented. If not, you’ll see the message “Target Device ID (0x0) is invalid.” To resolve this, just flip the cable.

On your custom board:

• Connect the SBU1 line of the USB-C port to the MCU’s RESET line.
• Connect the SBU2 line of the USB-C port to the MCU’s power supply (typically 3.3V).

The compatible debugging devices for this board include:

• The PICKIT3 or newer models, which connect via the right-angle SIL connector (designated as J3).
• The ICD4 or newer models, which connect through the RJ45 port (designated as J2).

ALL OF THE COMPONENTS ON THIS BOARD ARE THROUGH-HOLE.

The interconnection table, schematic, and layout can be found in the following section. A board similar to this one, but for an STM32-type MCU is showcased on this GitHub page: https://github.com/minoseigenheer/SWD-over-USB-C

Working Principle:

To signal the target device to enter debug mode, both CC1 and CC2 (Configuration Channels) must be pulled high. The USB-C connector has a total of 24 pins, with 10 dedicated to Vbus (power), GND, and CC (Configuration Channels). This leaves 14 pins available for manufacturer-specific port configurations in debug mode.

Standard USB-C cables connect a single CC line to determine the plug’s orientation. The host’s pull-up resistor sets the maximum current draw (e.g., 56kΩ to 5V for 500mA), while the device pulls the CC line down with a 5.1kΩ resistor to enable power delivery from the host. For Debug Accessory Mode (DAM), both CC lines need to be pulled high.

The official DAM resistor values are a bit different.

For 500mA @5V 22kΩ on CC1 and 10kΩ on CC2 should be used.

• CC1: Host 22kΩ pull-up to 5V and device 5.1kΩ pull-down = 0.9V
• CC2: Host 10kΩ pull-up to 5V and device 5.1kΩ pull-down = 1.7V

How to use:

1. Connect either the PICKIT or the ICD to the corresponding input on both the board and your computer. The first pin of the PICKIT, marked by an arrow, must be connected to the first pin of connector J2, which is indicated by a square-shaped pad.
2. Attach the USB-C cable to connector J4 and your board
3. External power can be provided via the connector J1 (5V IN).
4. Set switch S1 to the ON position. Once power is supplied to the board, the LED will illuminate.
5. Open MPLAB X IDE and flash your device.