Silicon Laboratories SI2493/57/34/15/04, SI2494/39 Implementing the Ademco Contact ID Protocol

AN93

8.2. Implementing the Ademco® Contact ID Protocol

Contact ID is a communications protocol for security applications. It is a de facto standard which was developed and is owned by the Ademco Group. The following is a brief overview of the Contact ID protocol. The complete standard is available at the following web site:

http://webstore.ansi.org/RecordDetail.aspx?sku=SIA+DC-05-1999.09

Communication is between an alarm panel and a central station. The part of the alarm panel that handles communication has the following functions:

Call the central station

Wait for the central station to indicate that it is ready for data

Send data

Wait for the central station to indicate that data was received

The central station also has a block that handles communication. Its functions are:

Answer calls

Acknowledge that it is ready to receive data

Receive data

Acknowledge that data was received

While performing their security functions, the communication part of the alarm panel always sends data, while the communication part of the central station always receives data. They are called the transmitter and receiver, respectively. (Data could flow the other way, for instance to download new firmware to the alarm panel, but this isn't covered by the Contact ID Protocol.)

A transaction begins with the transmitter calling the receiver. The receiver goes off-hook and acknowledges that it is ready to receive data by producing the handshake tone sequence:

1400 Hz tone for 100 ms

Pause for 100 ms

2300 Hz tone for 100 ms

The frequency tolerance on the handshake tones is ±3%. The tolerance on tone and pause times is ±5%. Transmitters have a frequency tolerance of ±5% to account for older receivers.

After the communication channel has been established, the transmitter sends data to the receiver in Message Blocks. Data is transmitted as DTMF codes. The frequency tolerance of the DTMF tones is ±1.5%. Twist is not specified by the Contact ID protocol standard.

After sending the message, the transmitter waits for the receiver to send an acknowledgement (Kissoff) tone. The Kissoff tone is a 1400 Hz tone that lasts for at least 750 ms and at most 1 second. The frequency tolerance of the Kissoff tone is ±3%; transmitters have a frequency tolerance of ±5% for back compatibility with old receivers. The receiver must detect at least 400 ms of the Kissoff tone for it to be considered valid.

The transmitter waits for the Kissoff tone to end, then waits an additional 250 to 300 ms before sending another Message Block. If no Kissoff tone is received after 1.25 s, the transmitter sends the message again. Up to four retries are attempted per Message Block. After the last message block has been acknowledged, the transmitter hangs up.

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