VAV Controller—Variable Air Volume (VAV) Controller 49
The Zone Bus is a 2-wire communications bus that allows a computer to
communicate with the VAV to download the VAV’s data base and to
communicate with Zone Terminals and M100 Actuators. A third wire is
used for 24 VAC power to the CBLPRO, Zone Terminal, and CBLCON.
The bus interface sustains no damage in presence of fault voltages of
24 VAC.
M100C Actuators must be powered with separate transformers; therefore,
only the Zone Bus and Common wires need to be pulled.
The Zone Bus has the following specifications:
Table 15: Zone Bus Specifications
Type
Multidrop serial communications bus
Speed
1200 baud (bits per second)
Recommended Cable Type
18 AWG/1.5 mm
2
with shield (Beldon 8760) or
24 AWG/0.6 mm diameter with no shield
(unshielded telephone cable)
Maximum Bus Length
500 feet/150 meters with 18 AWG/1.5 mm
2
cable or
50 feet/15 meters with 24 AWG/0.6 mm diameter cable
Range of Addresses
0 to 63
Voltages
Logic High-Voltage
Logic Low-Voltage
4 VDC minimum (approximately)
1 VDC maximum (approximately)
Data Transmission
1 Start Bit (low level)
8 Data Bits (least significant bit first)
1 Stop Bit (high level)
The VAV110/111 and VAV140/141 Series Controllers contain an LED
that blinks to indicate Zone Bus activity with or without external
connection. When a PC via CBLPRO communicates with the controller,
the blink rate may appear to be more steady. See Table 37: Zone Bus LED
Indications in the Troubleshooting section of this document for more
information.
69F70F71FZone Bus
Communications
Zone Bus
Description
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