Biamp A4 User Manual download pdf (Page 32)

Nexia-Manual-A4

Logic Box behavior can be altered using Logic Gates. Please refer to the

'Installation Guide

' (included with controls), or see Remote Control Bus for

more information. External controls must be identified (see Device

Maintenance) and associated with their corresponding component blocks

within the layout (see Equipment Table

Up to 20 logic inputs are availble on the Logic Box. Logic inputs allow remote control of NEXIA

via external circuits such as switches, relays, and logic outputs from other devices. When

nothing is connected to a logic input, an internal pull-up resistor keeps it at a 'high' state (+5.0

VDC). The logic input is activated when its input goes 'low' (less than +0.8 VDC), and is de-

activated when its input goes 'high' (greater than +2.0 VDC). A logic input can be controlled in

one of three ways: 1) Using an 'open-collector' or 'open-drain' logic output from an external

device to short the logic input to ground. 2) Using a switch, relay, or other contact-closure to

short the logic input to ground. 3) Using an active 5V TTL output driver circuit (such as from a

third-party controller) to actively drive the logic input to a 'high' or 'low' state. Multiple contact-

closures or 'open-collector'/'open-drain' logic outputs may be wired in parallel to a single logic

input (see diagram below). Open-collector or open-drain logic outputs and contact-closures

should be rated for at least 5 Volts / 1mA operation. Active output driver circuits should not

exceed a signal range of 0~5 Volts DC, and should have a minimum pulse width of 10 milli-

seconds. The logic input impedance is approximately 10k ohms.

The Logic Box provides up to 20 logic outputs. Logic outputs can be used to control relays and

indicators or to drive logic inputs of other devices. The Logic Box logic outputs are 'open

collector' with an internal pull-up. Each logic output is an NPN transistor with the collector being

the output and the emitter being ground (see diagram below). When a logic output is turned on,

the transistor provides a path for DC current to flow, lowering the output voltage to below 0.8V.

When a logic output is turned off, the internal pull-up resistor raises the output voltage to near

5V, depending on the output current. To activate external relays or indicators, an external power

supply must be used (see diagram below). The logic output transistors are rated up to a

maximum of 40 VDC and 500 mA per output (24 volt relay coils maximum). However, +12 Volts

DC is sufficient power for most applications. When using the logic outputs to control relays,

protection diodes must be used to suppress high voltage transients that are generated when the

relays turn off (see diagram below).

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Biamp A4 User Manual Page 32