N-1000-III/IV
6-14
6-14
6-14
6-14
6-14
Section 6: Wiring Requirements
Section 6: Wiring Requirements
Section 6: Wiring Requirements
Section 6: Wiring Requirements
Section 6: Wiring Requirements
6-6-8: Bias and EOL with 485 Communication
Bias voltage, provided by “pull up/down” resistors (bias resistors), is required for
the greatest clarity in 485 transmissions. At least one bias resistor must be con-
nected to a given drop line. In addition there must be an end of line resistor (EOL)
at both ends of the copper wire on a drop line for units to function efficiently.
Bias and EOL resistors are built into the N-1000-III/IV panel, the PCI, HUB and API
units. On the PCI and HUB, bias and EOL are present on the line when the green/
white wires are attached. With the API, bias and EOL are present when proper
attachments are made to pins 1 and 2 on TB2 (Refer to TD1077, N-485 Communi-
cation Adaptor Installation Guide that comes with the N-485-API-2.)
The N-1000-III/IV can provide bias for the PCI, HUB and API units when they are
not at the end of the line. Bias and EOL resistors on the N-1000-III/IV are attached
by using the proper jumper settings. Setting JP2 and JP3 on provides both bias and
EOL, while setting JP4 on provides EOL only. When JP2 and JP3 are on, JP4 must
be off.
Refer to Figure 6-13 for examples of bias and EOL.
Rule of Thumb for end of line termination (EOL).
1. EOL at both ends of copper.
2. Only one N-1000-III/IV panel, PCI, HUB or API provides 485 line bias. Bias is
provided when the green/white wires are used on the PCI and HUB, when
attachments are made to pins 1 and 2 on TB2 on the API or when JP2 and JP3
are used on the N-1000-III/IV panel. JP4 must not be used at the same time as
JP2 & JP3.