Data processing equipment in the office, on the factory floor and across
the campus may come in a variety of 'flavors,' embracing terminals,
badge readers, alarm equipment and all types of manufacturing and
laboratory instruments. The serial EIA's RS-232 interface is perhaps the
most widespread interface found on different data devices. It is perhaps
the most universally found debarkation point for bringing data into and
out of these devices. Data communication connections between such
equipment in the premises environment can often be accomplished by
merely connecting interfaces together by a cable.
One problem arises though. While the RS-232 interface is the most
widespread interface, it is not ubiquitous. There are other interfaces
notably, RS-422, RS-485, EIA-530 and still others. The need often arises
to interconnect data devices having different interfaces. Usually this
need is to interconnect a device having the popular RS-232 interface
with a device having something else like EIA-530.
In particular, let us focus our attention on the EIA-530 interface. Its
employment has been steadily spreading.
EIA-530 is a standard for signal and mechanical assignment
specification. The electrical specifications are the same as RS-422.
EIA-530 serves as a complement to RS-232D for data rates above 20 KBPS.
EIA-530, together with RS-422A and EIA-423, provides a convenient means
of implementing the higher data rates using the same mechanical
connector as specified in RS-232D. It is intended that EIA-530 gradually
replace EIA-449, which called for a 37 pin mechanical connector. As
such, EIA-449 was not well received by US industry.
EIA-530 has become very popular for US Dept. of Defense data
communications applications. Within the DOD it has the designation of
MIL-STD-188-114. There 2 category circuits under this designation,
Category I and Category II. With Category I, signals are differential -
like RS-422. With Category II, signals are single ended.
The Models 62-1/2 are ideally suited devices for converting between the
RS-232 interface and the EIA-530 interface. The two models differ in
only one relatively minor attribute. The Model 62-1 has an RS-232 port
configured to connect to a DTE. The Model 62-2 has an RS-232 port
configured to connect to a DCE.
Otherwise, the Models 62-1/2 are fully compliant with EIA-530 and with
RS-422. They meet MIL-STD-188-114 Type 2. They allow data to pass
through at a rate of 256 KBPS. They support 10 Category I circuits and 3
Category II circuits.
The Models 62-1/2 are stand-alone units. In some situations it may be
more convenient to have them as cards mounted in a card cage. Card cage
mounting may be more convenient for the environment where you have a
single computer communicating with many data devices spread throughout
the premises. Cabling mess can be avoided and power supply cost can be
reduced by rack mounting card versions of modems in a cage and placing
the cage in a 'communications closet.' Spare cards can also be placed in
the cage in case of failures. Reliability is thereby increased.
The Model 267-1 is a card version of the Model 62-1. The Model 267-2 is
a card version of the Model 62-2.
The illustration above shows an application with the Model 62-1/2 and
Model 267-1/2. Here we have a Multi-user computer on the left
communicating with number of different Computer Work Stations on the
right. The interfaces at both the Multi-user computer and the Computer
are RS-232. However, RS-232 does not use differential signaling. If
differential signaling were used the data communication would have the
extra protection from interference and extended distance. EIA-530 as
MIL-STD-188-114 Category I is differential.
This illustration indicates a number of different RS-232 ports at the
Multi-user computer being converted to MIL-STD-188-114 Category I on the
left. Here the Models 267-1/2 are being used in a card cage. This is
most convenient since a number of different conversions are being done
at this same Multi-user computer location. The choice of Model 267-1 or
Model 267-2 depends upon whether the port looks like a DTE or DCE. The
cards are shown mounted in a Model 76-7 card cage.
On the right hand side of the illustration you can see the conversion
back to RS-232 from MIL-STD-188-114 Category I being carried out,
separately, at each Computer Work Station. The stand-alone Models 62-1/2
are appropriate here.