7 A1000 & A2000 USERS MANUAL
should be placed at each end of the RS-485 cable. Please refer to Figure
2 for a typical RS-485 system application.
The A1000 and A2000 each contain the biasing and termination resistors
necessary to interface any equipment on an RS-485 network. These
resistors are switch-selectable making it easier to interface the A1000 and
A2000 to other pieces of equipment that may or may not contain the
biasing and/or termination resistors.
Figure 2. RS-485 biasing & termination resistors.
A 1 0 0 0 R S - 4 8 5 T E R M I N A T I O N S
Each A1000 contains internal RS-485 termination and biasing resistors
for proper termination of a RS-485 system. The resistors are enabled or
disabled via two 3-position DIP switches located on the A1000 rear panel.
One three-position switch enables termination resistors for the RS-485 IN
(HOST) data lines and the other switch enables termination of the RS-
485 OUT data lines. The three-positioned DIP switches are located to the
left of each RS-485 connector on the A1000 backpanel. The three
positioned switches are used to enable or disable a 1K
Ω
pull-up between
+5Vdc and the DATA+ line, a 1K
Ω
pull-down resistor between the DATA-
line and ground or a 220
Ω
termination resistor between the DATA+ and
DATA- lines. Each switch is labelled +1K, -1K and 220. Set the
appropriate switch to the "up" position to enable a resistor.
NOTE: The RS-485 IN +1K and -1K switches should be "up" when the
A1000 is used as a RS-232/RS-485 converter.