Abstract: The present invention provides a reliable communication protocol that provides multicasting of digital messages on an interprocessor link coupling together a plurality of processors of a load control system. Preferably, the load control system includes a plurality of sub-systems, with a number of the processors in each sub-system. The processors are each characterized by a unique individual address, while all of the processors of a single sub-system are characterized by an identical multicast address. The processors re-transmit digital messages on the communication link if a target address of the digital message is equal to the multicast address. The processors determine if acknowledgement messages are received from each of the processors from which acknowledgement messages were expected during a predetermined amount of time after transmitting an initial digital message, and transmit a retry message in response to determining that the acknowledgement messages were not received.

Abstract: A lighting control system having a plurality of control devices coupled to a communication link operates with a communication protocol that allows the system to expeditiously process high-priority events while operating communicate at a low enough baud rate to allow for a free-wiring topology of the communication link. The transmission of regular-priority messages is suspended if any of the control devices has a high-priority message to transmit. To signal that a control device has a high-priority message to transmit, each control device is operable to transmit a break character in a predetermined time period after the transmission of one of the digital messages. After the transmission of the break character, the transmission of the regular-priority messages on the communication link is suspended to allow the high-priority message to be transmitted quickly.