Appendix D - The Rci Rs-422 Interface Specification - Dawn CONTROL-1500A Manual

CONTROL-1500A Single Axis Antenna Controller Appendix D The RCI RS422 Interface Spec 64

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.
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