Athena 6075 series, Instruction Manual, Page: 30 / 39

SECTION 6 COMMUNICATIONS
6.1 Communications
Modules
Optional plug-in modules are available for the Series 6075 to allow interfac-
ing to the most common industry standards. A brief description of each type
follows.
6.1.1 RS485
RS485 is a specification standard for balanced voltage digitial interface cir-
cuits published by the EIA.
It was published in 1983 as an upgrade of RS422A electrical specifications,
with emphasis given to the application of multipoint systems. The interface
circuits used in
the Athena
Model 6075 meet the electrical characteristics of
the RS485 standard.
The RS485 multipoint capability allows up to thirty-two (32) units to be con-
nected together in a half duplex network More can be added with the use of
“repeaters” such as the Athena Model CC.1 interface box
This module allows bi-directional data transfer over a shielded twisted pair.
The twisted pair is a transmission line with drops to communicating devices.
Since it is a transmission line, terminating resistors are required at the most
distant ends of the line to minimize reflections. (Typically 60 ohms from
each line to signal ground).
The Model 6075 RS485 module is fully optically
isolated, eliminating ground loop problems, Parallel drops from the
transmission line should be kept as short as possible. Alternately the line
could be daisy chained at each DB-9 connector. Note that the polarity of the
line is important and each device will
specify
an “A” and ”B” connection. On
the 6075 RS485 module, “A" is pin 8 and 4; “B” is pin 7 and 3 and com-
munications ground is available on pins 1,2, and 6. Frame ground is pin 5
and 9.
6.1.2 RS232C
The RS232C is a standard that was published in 1968 by the “Electronic
Industries Association” (ElA). The RS is an acronym for Recommended
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