Connection and wiring
One-way bus installation
The RS-485 transmission line must be connected in a daisy chain configuration as shown in Figure 1. In a daisy chain configuration, the transmission line connects from one RS-485 receiver to the next. The transmission line appears as one continuous line to the RS-485 driver. A branched or star configuration is not recommended! This method of connection appears as taps or stubs to the RS-485 transmission line. Stub lengths affect the bus impedance and capacitive loading which could result in reflections and signal distortion.
FIGURE 1: One-Way Bus Installation
Split bus configuration
The RS-485 Output may be split in two directions as shown in Figure 2. This allows the master clock or time server to be centrally located. Connecting in this method can simplify installation and possibly reduce the amount of cable required.
FIGURE 2: Split Bus Configuration
Connection and strain relief
Most RS-485 connections found on Spectracom equipment are made using a removable terminal strip. Wires are secured by a jaw which compresses the wires when tightened. When using small diameter wire, 22-26 gauge, a strain relief can be fashioned by wrapping the stripped wire over the insulating jacket as shown in Figure 3. Wrapping the wires in this manner prevents smaller gauge wires from breaking off when exposed to handling or movement. TimeView display clocks use a 6-position terminal block to connect to the RS-485 data bus. Devices such as the model 8185 TimeBurst audio interface to a transmitter for wireless time distribution and models 8188 and 9188 Ethernet Time Servers, use a 3-position terminal block to connect to the RS-485 data bus. Connect all of these devices to the Remote Output as shown in Figure 3.
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FIGURE 3: WIRE STRAIN RELIEF |