Rear Panel Assembly; Logic And Chassis Ground - Honeywell LC13-510 Manual

2.5 REAR PANEL ASSEMBLY

The Rear Panel Assembly includes the Backpanel Printed Wire Assembly (PWA) and the
Input/Output (I/O) Card Cage Assembly. The power supplies, the fan assembly and the
main circuit boards (such as the K2LCN OR K4LCN) all plug into card edge connectors on
the front side of the Backpanel PWA. The I/O boards all plug into card edge connectors on
the rear side of the Backpanel PWA. As shown in Tables 2-2 and 2-3, the I/O boards are
normally installed in the chassis in the slot corresponding in number to the applicable board
installed in the front of the node. The CLCNA (KLCN-A ) and CLCNB (KLCN-B)
boards are installed as shown in Table 2-1. The various I/O boards support interface to a
variety of external networks and devices such as the LCN, Data Hiway, keyboards,
monitors, disk drives, and recorders.
Other connections available at the rear panel assembly are:
• Ac Input—The ac input cable for each power supply terminates in a receptacle
which is attached to the backpanel support at the rear of the power supply. The
power supply plugs into the receptacle when it is inserted into the chassis. The
receptacles pass through, but do not connect to, the backplane.
• Remote Reset—There is a 3-pin connector soldered to the backpanel for each
node which permits the node to be reset by a remotely-located switch.
• External Clock—There is a 2-pin connector soldered to the backpanel for each
node which allows use of an external precision clock source for the system
clock.
• RS-485 Connectors—The RS-485 bus communicates the LCN A and B signals
between the two nodes in a Dual Node Module. There are connectors at the upper
and lower ends of this bus. They provide a place to install resistor terminator
assemblies. Two terminator assemblies are installed at the top and two are
installed at the bottom.

2.6 LOGIC AND CHASSIS GROUND

There are two threaded posts for logic ground on the Rear Panel Assembly – one behind
each power supply. In most applications, logic ground is connected to chassis ground, and
this connection is made by installing a jumper wire between the logic ground post and the
rightmost mounting screw of the Ac power connector. This connection is made for both
nodes in the module. Figure 2-7 and Figure 8 shows these logic-to-chassis ground
jumpers installed in two modules. If isolated logic ground is required, the jumpers are not
installed. Note that both nodes have a common logic ground through the RS-485 bus, and
therefore a single node cannot be ground-isolated by itself. Both nodes must be either
connected to chassis ground or isolated from chassis ground, but they cannot be ground-
isolated with respect to each other. If the nodes are to be isolated from chassis ground,
both jumpers must be removed.
There is also a threaded hole on the Rear Panel Assembly. This is a connection point for
chassis ground.
Figure 2-2 also shows the location of the logic ground and chassis ground points on the
Rear Panel Assembly. These connection points are also physically marked for
identification on the Rear Panel Assembly.
Dual Node Module Service 2-16
2.5
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