Honeywell VC4 User Manual page 177

Impedance Matching
The communication interfaces in the first and last units in the daisy-chain configuration must
have matching impedance. This is true whether the computer is at the end of the daisy chain or
within the daisy chain. Check the computer's interface to determine the impedance termination
resistor's value and how to install/set. The illustrations below show two daisy chain schemes,
the first with the computer on the end of the daisy chain, and the second with the computer
within the daisy chain. The impedance termination resistors on all interfaces between the first
and last units are removed.
Configuration showing Computer at one end of a Daisy-Chain
Configuration showing Computer in the middle of a Daisy-Chain
The VC4™ unit's impedance termination resistor is located on the RS-485 interface as shown
below. The resistor plugs into sockets on the interface board for easy removal or insertion; there
is no soldering required.
VC4™ RS-485 Interface Board Impedance Resistor Location.
VC4™ 177 User Manual