ETS 2604
CyberResearch
®
Serial Communications
2
©Copyright
2008
CyberResearch, Inc.
Card Setup
Electrical Interface Selection
Each port on the
ETS 2604
has the ability to be used in either RS-232 or RS-422/485. This is selectable using the
software setup utility and correctly configuring DIP-switches S1-S4.
RS-485 Enable Modes
RS-485 is ideal for multi-drop or network environments. RS-485 requires a tri-state driver that will allow the
electrical presence of the driver to be removed from the line. The driver is in a tri-state or high impedance condition
when this occurs. One of the unique features of the
ETS 2604
is the ability to be RS-485 compatible without the
need for special software or drivers. This ability means that the user can effectively use the
ETS 2604
in an RS-485
application with the standard CyberResearch Software supplied drivers.
Typically, each end of the RS-485 bus must have a line-terminating resistor (RS-422 terminates the receive end
only). A 120-ohm resistor (silk-screen ‘T’) is across each RS-422/485 input in addition to a 1K-ohm pull-up (silk-
screen ‘PU’) and a 1K-ohm pull down (silk-screen ‘PD’) combination that biases the receiver inputs. Only the ends
of an RS-485 network should have the 120-Ohm terminating resistor. The presence of the 120-Ohm termination
resistor across the input data pins (RX+/RX-) as well as the pull-up and pull-down resistors may be removed or
inserted with DIP-switches S1-S4. To add the termination/bias resistors select the ‘On’ position, to remove it select
the ‘Off’ position.
1
2
3
4
5
6
7
ON
OF
F
8
EN
T
PD
PU
EN
T
PD
PU
RS-232
1
2
3
4
5
6
7
ON
OF
F
8
EN
T
PD
PU
EN
T
PD
PU
RS-422/485
1
2
3
4
5
6
7
ON
OF
F
8
EN
T
PD
PU
EN
T
PD
PU
RS-422/485 No termination
