SIA PID-01-1995.12 (2000.06) | SIA Point Identification Multiplex Protocol - Security and Life Safety Applications - Addressable
Scope and Benefits
This standard defines the SIA protocol for addressable multiplex, sensor, control and annunciation modules for Security and Life Safety systems. This protocol utilizes two way digital transmission scheme, which can be implemented at low cost over a two wire trunk. The trunk also supplies power to the remote devices.
The protocol command set and response data allows highly reliable, error resistant transport of both analog and digital messages with fast response mode for any sensor or device in the alarm condition.
Devices may be interfaced to the trunk in any order in a single ended or loop configurations.
This protocol has been designed to work in life safety, security, and combination life safety and security systems. The protocol incorporates: an 8 bit address field, 16 different bus cycle codes, a priority alarm capability, expansion field, 256 different device types (each with 4 control and 4 status bits), an 8 bit analog data field, and extensive error detection through address echoing, double polling and a Cyclic Redundancy Check (CRC).
The analog addressable protocol allows sensors (remote units) to be connected to a 12 or 24 Volt two-wire multiplexed trunk that carries both power and data between the control panel and the remote units. This trunk may be configured as a class A (fault tolerant ring) or class B. Spurs or "T" taps are allowed. Sensor addresses can be in any order. Average normal power consumption in this two wire configuration should be less than 1 mA per sensor and the maximum normal trunk current should be less than 100mA otherwise the total reach of the systems may be severely limited by the ohmic drop of the cable.
A two-way communication link is established by voltage Pulse Code Modulation (PCM) from the control unit and synchronous current pulsing from the remote units. The communications between the panel and remote units is set up as a master/slave link which consists of the panel polling a particular address or group of addresses followed by the synchronous response of the addressed unit. All actions of the remote units are controlled by the control panel. This allows the control panel to continually monitor the presence and functionality of all attached units, and to modify the alarm processing algorithms as needed per location. The address of each remote unit is an 8 bit value that is programmable. Each device responds to the control unit by executing commands, sending digitized sensor readings, and confirming local addresses. The sensor readings sent back to the control unit are the present analog output of the sensor in a digitized format. Or in the case of a non-analog device, is an 8 bit value indicating the present sensor status. Data transfers between the control unit and the remote unit are validated through the use of a 4 bit CRC, and an address echo data field. All commands to the remote unit will be further validated through the use of double polling. Since the remote units recognize their own address, interrogation of the units can be done in any order.
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