SECTION 4 – LCN CLOCK SYSTEM
4.5 Remote Segment Clock Requirements
Remote K2LCN node
cable segment The need to transmit a system clock between LCN coaxial cable segments is mandatory to guarantee the accuracy of alarm events, specifically Sequence Of Events (SOE) alarms. If the remote cable segment requires only a 5 Mbits/second digital clock because K2LCN nodes are present, and the central cable segment can generate this clock through a K2LCN node, additional hardware is not required. Figure 4-4 is an illustration of an LCN configuration that does not require transmission of the 12.5 kHz system clock to a remote cable segment.
Table 4-5 contains a name and description of the basic nodes used in the remote K2LCN node segment combined clock configuration.
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4.5 Remote Segment Clock Requirements,
ContinuedFigure 4-4 Remote K2LCN Node Segment Combined Clock System Configuration
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I H (K2LCN)Node G (K2LCN)Node F (K2LCN)Node Cable B
Table 4-5 Remote K2LCN Node Segment Combined Clock System Configuration Nodes and Definitions
Configured as the 12.5 kHz master clock source, the node is loaded with operating software first. The node provides a clock to its CS/R board for transmission of the 12.5 kHz system clock that is superimposed on the 5 MHz data signal in LCN cable A. After the node is established as the master clock source, it does not listen. The node assumes responsibility as the slave clock source when it has recovered from a failure.
The node is configured as a clock source and loaded with operating software after the master clock source node is loaded. After the operating software is loaded in the node, the node detects the master clock and synchronizes its clock. The node provides the clock data that is transmitted by its CS/R board in LCN cable B. If the master clock source fails, the node declares itself the master clock source and does not listen.
These nodes listen for the clock messages in both LCN cables. The nodes synchronize themselves with the master clock messages.
Assume this is the first K2LCN node to be loaded with operating software after nodes A and B are loaded. The node first listens to both LCN cables for a digital clock
synchronization message. If none are detected, it listens for the 12.5 kHz system clock signal. When the 12.5 kHz system clock is detected, the node synchronizes its clock with the master clock and becomes a 5 Mbits/second digital clock translator for other K2LCN node listeners in the LCN.
Assume that these nodes are loaded with operating software after the node F becomes a clock translator. They listen for digital clock synchronization messages on both cables and synchronize their clocks using the messages from node F.
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4.5 Remote Segment Clock Requirements,
ContinuedRemote non-K2LCN
node cable segment If the remote cable segment requires a 12.5 kHz system clock because it has non-K2LCN nodes and the distance to the remote cable segment exceeds 300 meters, fiber optic clock transmitter and receiver boards (FOC/XMTR and FOC/RCVR) must be used in addition to the CS/R boards and LCN Extender (LCNE) boards. Should the distance to the remote cable segment be less than 300 meters, optionally the 12.5 kHz system clock can be transmitted directly over twisted pair current loops between CS/R boards.
Refer to Section 5 for additional information on fiber optic links and twisted pair current loops.
Remote non-K2LCN node cable segment illustration
Figure 4-5 is an illustration of a typical LCN configuration that requires transmission of a 12.5 kHz system clock to a remote cable segment over a fiber optic link.
Table 4-6 contains a name and description of the basic nodes used in the remote non-K2LCN node segment combined clock configuration.
Figure 4-5 Remote Non-K2LCN Node Segment Combined Clock System
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4.5 Remote Segment Clock Requirements,
ContinuedDefinitions
Table 4-6 Remote Non-K2LCN Node Segment Combined Clock System and Definitions
Node Name Description
Node A
Node B
Nodes C, D, E Node F
Nodes G, H Nodes I, J
Configured as the 12.5 kHz master clock source, the node is loaded with operating software first. The node provides a clock to its CS/R board for transmission of the 12.5 kHz system clock that is superimposed on the 5 MHz data signal in LCN cable A. After the node is established as the master clock source, it does not listen. The node assumes responsibility as the slave clock source when it has recovered from a failure.
The node is configured as a clock source and loaded with operating software after the master clock source node is loaded. After the operating software is loaded in the node, the node detects the master clock and synchronizes its clock. The node provides the clock data that is transmitted by its CS/R board in LCN cable B. If the master clock source fails, the node declares itself the master clock source and does not listen.
These nodes listen for the clock messages in both LCN cables. The nodes synchronize themselves with the master clock messages.
Assume this is the first K2LCN node to be loaded with operating software after nodes A and B are loaded. The node first listens to both LCN cables for a digital clock
synchronization message. If none are detected, it listens for the 12.5 kHz system clock signal. When the 12.5 kHz system clock is detected, the node synchronizes its clock with the master clock and becomes a 5 Mbits/second digital clock translator for other K2LCN listener nodes in the LCN.
Assume that these nodes are loaded with operating software after the node F becomes a clock translator. They listen for digital clock synchronization messages on both cables and synchronize their clocks using the messages from node F.
These non-K2LCN nodes in a remote cable segment receive and transmit the LCN 5 MHz data signal through the fiber optic LCNE boards. The 12.5 kHz system clock for the remote cable segment is detected by the FOC/RCVR boards, also through fiber optic links. FOC/XMTR boards transmit the clock for the remote segment LCN A and B cables.
The clock that is detected by the FOC/RCVR boards is synchronized and transmitted to the CS/R boards where it is retransmitted into the A and B cables.
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