AS-P
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Hardware Installation
Hardware Installation
Part number: SXWASPSBX10A01
Hardware Installation
Part number: SXWTBASW110A02
Hardware Installation
Hardware Installation
Hardware Installation
Part number: SXWTBASW110002
Hardware Installation
Concept
The recommendations include two different configuration options to choose from with differences in performance and/or resources required.
Concept
Dual end-point bias applies a separate 5 V DC supply at each end of the network to generate the RS-485 bias. Instead of a single pair of 510 ohm resistors, the dual end scheme uses a pair of 1000 ohm resistors at each end. The dual end-point is the best technique for avoiding the drop in the bias voltage over extended cable lengths as you move away from the bias connection location. By applying bias at the two termination points, the arrangement maintains an equal bias across the complete length of the cable.
Concept
This configuration is the simplest to arrange and supports bus lengths out to 150 m (500 ft) on 24 AWG (0.20 mm²). The automation server should be configured with two 510 ohm bias resistors. One resistor connecting the + data line to the Bias+ terminal on the automation server and the other resistor connecting the – data line to the RET terminal on the automation server. The bias is required to support the transceivers in the VT/VZ nodes and the termination of the bus. AS-P servers and AS-B servers provide 5 V for bias, which supports 120 ohm termination resistors at the two ends of the bus. This will achieve the minimum idle line bias voltage of +200 mV required by the transceivers. Low resistance bias configurations (with 5 V supplies) add significant common mode load on the RS-485 network. The common mode load (Unit Load) of the bias network must be summed with the accumulated unit load of the collection of VT/VZ thermostats/controllers to identify the total unit load on the bus.