---
title: "Core B2B v2"
canonical_url: https://developer.repebble.com/pebbleos/docs/programmers/core_b2b_v2/
last_updated: 2026-10-21
sdk_version: 4.33.1
---
# Core B2B v2

Source: https://developer.repebble.com/pebbleos/docs/programmers/core_b2b_v2/

The Core B2B v2 is the programmer of the Pebble 2 Duo firmware development kit. It plugs into the watch’s B2B (board-to-board) connector and gives a host SWD debug access and the debug UART over a single USB connection.

Boards:

[asterix](https://developer.repebble.com/pebbleos/docs/boards/asterix.md)

Host interface:

USB: CMSIS-DAP probe and virtual COM port

Target interfaces:

SWD, debug UART, reset, VUSB

Runners:

`openocd`, `nrfutil`

Firmware:

[coredevices/asterix\_b2b2\_fw](https://github.com/coredevices/asterix_b2b2_fw)

It is based on the [Raspberry Pi Debug Probe](https://www.raspberrypi.com/documentation/microcontrollers/debug-probe.html).

## Features

![../../_images/core-b2b-v2-board.webp](https://developer.repebble.com/pebbleos/docs/images/core-b2b-v2-board.webp)
_Core B2B v2_

The flex cable on the left goes to the watch’s B2B connector.

1. USB connector

2. Debug UART routing

3. SWD routing

4. Debug UART pins

5. External SWD connector

6. MCU reset

7. VUSB switch

Warning

External connectors (SWD/UART) expose 1.8V signals. Do not use any adapter that does not operate at 1.8V, or there is a **risk of damage**!

## Usage

Before first use, update the programmer to the [latest firmware release](https://github.com/coredevices/asterix_b2b2_fw/releases).

To use the built-in CMSIS-DAP probe and USB-UART converter, place switches (3) and (4) to the right. Provide VUSB while programming, so the watch stays programmable regardless of its battery level, by placing switch (8) to the left:

![../../_images/core-b2b-v2-switches.webp](https://developer.repebble.com/pebbleos/docs/images/core-b2b-v2-switches.webp)
_Switches set for the built-in probe and USB-UART converter, with VUSB provided_

The board page explains how to connect it: [Pebble 2 Duo (asterix)](https://developer.repebble.com/pebbleos/docs/boards/asterix.md).

## Troubleshooting

- If the watch cannot be programmed, check the switches; they sometimes move during shipping.

- If the serial console shows output but does not accept input, the B2B connector is not fully seated. Press it until it clicks.

Generated from PebbleOS [3a7b71785](https://github.com/coredevices/pebbleos/commit/3a7b71785fd439666c4a8bc116f561140e8dec01). This page is maintained in the pebbleos repository: [docs/programmers/core\_b2b\_v2.md](https://github.com/coredevices/pebbleos/blob/3a7b71785fd439666c4a8bc116f561140e8dec01/docs/programmers/core_b2b_v2.md).