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2.3 FRONT PANEL Controls on the front panel of the power supply consist of a POWER switch, a RESET button, a FAN CONTROL, and a LO-NOM-HI margin jumper. The function and operation of the power and reset controls are discussed elsewhere in this manual. The margin jumper is a power supply test/maintenance diagnostic aide and should be left in the NOM (center) jumper position at all times. The EC power supply contains a fan control switch/jumper and is set for either a thermally-controlled or fixed-fan power (see Figure 3-2). One setting varies the fan voltage with temperature and load. The other setting provides a continuous 27 volts. The front panel contains indicators that provide status of the unit’s performance and aid in fault isolation. The LED indicators on the bottom left of the front panel (the power supply) give an indication of the power-supply status. Another indicator on the fan assembly lights if the fan assembly fails. LEDs on each of the boards are used in conjunction with an alphanumeric display on the processor board to isolate malfunctions on the boards. Further information on the use of the module indicators is located in Section 3 of this manual. 2.4 REAR PANEL The rear panel contains the I/O boards (paddleboards), chassis power-cable, a 100-pin backplane breakout board (if provided), and a grounding lug. As shown in Table 2-1 the I/O boards are installed in the chassis in the slot corresponding in number to the applicable board installed in the front of the module. All communication with the Micro TDC 3000 is through the I/O boards. There are two methods of communicating between nodes on the system. The conventional LCNI I/O paddleboards form the Local Control Network with coaxial cables that run to all of the LCN nodes in a network. In the network, all LCN I/O boards are connected by T connectors and cable (or to a terminating load on the last T in a series). Because of loading characteristics, the minimum LCN cable length is 2 meters (6 feet), so there may appear to be some cable “waste” when nearby LCN boards are interconnected. In all LCN cabling, the I/O board connectors are marked A and B; make sure that the A cable connects to the A connector and that the B cable is connected to the B connector. A special short distance LCN network has been designed which uses twisted pair and multinode module backplane wiring instead of coaxial cable and T connectors. The I/O paddleboards used for this network are the TP485 boards. This twisted pair LCN cabling follows the RS 485 interface standard. One of the K2LCN processor boards and TP485 I/O cards in slot 9 of each tower supplies clock to other nodes on the short distance network. The twisted pair cables which tie this short distance LCN together are keyed so that cables A and B cannot be misconnected and terminating loads are built-in. Ribbon cables are used to connect to such items as the Winchester Drive, Cartridge Drive, and other peripherals. Other connectors, for example RS 232C or RS 449 on the Computer Gateway, are also used.