Systems and methods for communication between an implantable medical device and an external device. Data blocks are generated and transmitted between the implantable device and the external device. The data blocks include a first flag indicating whether the data block is a first data block in a message and when the data block is a subsequent data block in a multiple data block message. When the first flag indicates that the data block is a first data block in a message, the data block also contains a device ID, a command token, and message content. When the first flag indicates that the data block is a subsequent data block in a multiple data block message, the data block contains additional message content that is appended to message content from a previously received data block.