CITATION 7.0 BUS PROTOCOL
AUGUST 16, 1999
HOW DOES IT WORK?
The Citation Communication Protocol is designed specifically for controlling audio and video
equipment. It was developed in response to a need for a low-cost, simple, fault-tolerant
communications protocol. It is based on the EIA RS-485 electrical specification and utilizes
CSCD (collision sense, carrier detect) to allow multiple devices to send and receive data on the
same pair of wires. Data is communicated at 9600 baud, 8 data bits, 1 stop bit and no parity.
The command set is similar to CONDIY developed by Audioaccess. Citation and Audioaccess
products can share the same data bus. Additionally multiple 7.0?s may be connected on the
same data bus and communicated with by simply changing the Unit ID in the 7.0 and
addressing that ID when sending a command on the data bus.
Before beginning data transmission, the bus should be checked for inactivity. If the bus is free,
transmission may commence. If the bus is being used, wait for a period of inactivity. Each
transmission should be checked against the intended message, to ensure that data corruption
did not occur due to multiple devices attempting to use the bus at the same time. For each
data transmission not originating from the main controller, the main controller will automatically
generate an acknowledgment (38h) (i.e. any information coming into the main controller gets an
ACK). The device which sent the data should receive this acknowledgment before beginning
its next data transmission. Under rare circumstances, the main controller may be performing a
function which cannot be interrupted. The data should be retransmitted until an
acknowledgment is received. Due to this fact, delays are required between incoming
commands for the transmission of the required acknowledgment.
WHAT IS THIS DOCUMENT?
The first section of this document describes the structure of the code and what each byte
means. The second section demonstrates the construction of sample codes. The subsequent
sections list all of the available codes for each device type.
Citation Bus Protocol.doc Page 4 |
ACEC
