OpenCM 9.04 by Robotis
The OpenCM9.04-C is the same as the OpenCM9.04-B except that the two TTL connectors (used for the AX series) have been replaced by two XL-Type TTL connectors (used for the XL-320). Both versions C and B are compatible with this firmware to connect with ARC. This controller is also used in the Robotis Bioloid Mini that can be controlled by ARC with these firmware.
OpenCM9.04 is an open-source controller that runs on a 32bit ARM Cortex-M3. The 3-Pin connector(XL-type) controls DYNAMIXEL XL-320 with TTL communication in ARC using the Dynamixel plugin. For AX & MX series Molex connectors, the OpenCM Expansion Board is needed
Robotis Dynamixel Robot Skill
The chances are that you're using this OpenCM 9.04 board with Robotis dynamixel servos. If that is the case, the Robotis Open CM9.04 controller can support servos connected directly to itself or through the expansion board. Using only the controller, UART #0 is used in ARC. If using the expansion board, UART #2 is used in ARC.