J-4
August 1999
76-100016-001
PEGAsys
Intelligent Suppression Control/Fire Alarm System
line. Each node uses one (1) NIC. The NIC performs the follow-
ing functions:
•
Dual Channel Support
•
Messaging
•
Repeater
•
Fail Safe
•
Isolation
TA1
ISOLATED
NETWORK MEDIUM
TA2
NON-ISOLATED
NETWORK MEDIUM
Hardware
Repeater
Logic
Rx/Tx Selection
Logic
1/2 NETWORK INTERFACE CARD (NIC)
To CCM CPU
TB2
TB1
Rx out
Rx out
Tx in
Tx in
Driver
Enable
Driver
Enable
RTS Rx
Tx
Figure J-3. NIC Block Diagram
(Shown With Power To NIC Lost)
J-4.2.1 DUAL CHANNEL SUPPORT
The NIC optionally supports operation of Style-4 or Style-7 chan-
nels. Under normal operation with Style 7, network communi-
cation is divided between the two channels. In case of a short
circuit or a break in any of the connecting wires, either channel
by itself can execute all network communications, although
somewhat more slowly than if both channels are in operation.
J-4.2.2 MESSAGING
When a node wishes to transmit over a network channel, the
data is written to the NIC which sends the signals out to the bus
for receipt by remote NICs. While a node is not transmitting
data, the NIC reads the bus data traffic, and converts it to a
form readable by the node’s software. Data communication will
be configured on the NIC’s UART as 8 bits, no parity, 1 stop bit
(8-N-1), and 9600 baud. The NIC will either transmit locally pro-
duced data or receive and retransmit bus activity as a repeater.
J-4.2.3 REPEATER (TRANSCEIVER)
The NIC acts as a repeater, regenerating bus information as it
moves through the NIC. Its bidirectional repeater function is
implemented completely in hardware; no software is needed to
control this process. The transceiver’s transmit and receive
switching (in half-duplex mode) is also performed automatically
by hardware.
J-4.2.4 FAIL SAFE
If a power failure occurs in a node, the NIC includes a normally
closed (NC) relay which maintains the communications integ-
rity of the network. When the NIC loses power, the relay passes
the network signals directly through the board. While the node
without power will not participate in networking, this pass-through
function allows all other network nodes to function normally while
providing the proper trouble indications.
J-4.2.5 ISOLATION
One half of each channel is an isolated, floating RS-485 trans-
ceiver and the other half is a non-isolated, grounded RS-485
transceiver. This assures that the chassis of any two nodes are
physically disconnected, eliminating the possibility of ground-
loop current, while retaining the ability to detect ground faults.
J-4.3
Network Wiring
The panels are networked by attaching two twisted, shielded-
pair cables between the appropriate NICs. The node-to-node
wire must not exceed a length of 4000 ft. and must be AWG 18
or heavier gauge. Under adverse conditions (for example, high
electrical noise) shielded twisted pairs may be required. Con-
nect panels together as shown in Figure J-4.
B1IA1
B2IA2
B1NA1
B2NA2
NETWORK
INTERFACE
CARD
CCM CPU BOARD
PEGAsys PANEL
PEGAsys PANEL
B1IA1
B2IA2
B1NA1
B2NA2
NETWORK
INTERFACE
CARD
CCM CPU BOARD
Channel 1
Channel 2
Note A
Note B
Note A:
Attach the shields on the 'N' side of the network line to the grounding screw on the CCM.
Note B:
Note C:
The shields on the 'I' side of the network line are to be cut short and left floating.
All circuits are supervised and power limited.
Figure J-4. Network Wiring
J-5
MAINTENANCE AND/OR REPLACEMENT
No maintenance is required. In the event of failure, the module
should be returned to the factory for repair or replacement.
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