Appendix D - The Rci Rs-422 Interface Specification - RESEARCH CONCEPTS RC2000C Manual

RC2000C Polar Tracking Antenna Controller Appendix E Communications Protocol 73

Appendix D - The RCI RS-422 Interface Specification

Introduction
The purpose of this document is to explain the key parameters needed by a user to interface to the RCI RS422
Interface. This interface is compatible with the SAbus and can be readily integrated into an existing SAbus
network. A few query and control commands are all that are needed to control the equipment and fetch all data
from it. The user should refer to RCI document 'Communications Protocol' for the specific program commands
and descriptions of their functions.
Electrical Specifications
RS-422 is a unipolar, balanced 5-volt serial interface designed to connect equipment which must exchange
data over considerable distances with high-noise immunity and high speed. Standard IC drivers and receivers
are available for RS-422 that convert to and from TTL logic levels. The RS-422 drivers/receivers in the
controllers allow up to 32 devices to be connected in parallel with up to 1,500 feet between the master and
group of controllers.
Physical Specifications
The physical implementation of the interface takes the form of a 9-pin "D" connector located on the rear panel
of the controller. This connector and its wiring is compatible with EIA RS-449, which is the mechanical
specification for RS-422/423-compatible equipment. The 9-pin connector chosen is described as the
secondary interface in RS-449 and has only the four data lines and shield. No hardware handshaking is used
in the protocol, so all the control lines specified for the standard 37-pin connector are not needed. The
controller operates as a slave only and has a female connector, whereas master devices have male
connectors. Multiple controllers, connected in a daisy chain fashion, can operate in electrical parallel with only
a single 5-conductor cable required to connect all devices controlled by a master. Figure 1 illustrates the
connection of a master and multiple controllers.
RS-422 Protocol
The interface is a multi-drop, balanced line, asynchronous, full-duplex communications link designed to
interconnect equipment for remote control and switching applications. Products that are compatible can be
linked together over a parallel-connected 4-wire circuit without regard to their particular function.
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