Model 365 Application Notes
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-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 EIA-232 interface is the most
widespread interface, it is not ubiquitous. There are other interfaces,
notably RS-422 and RS-485. The need often arises to interconnect data
devices having different interfaces. Usually this need is to
interconnect a device having the popular EIA-232 interface with a device
having something else like RS-422.
Interface conversion is a straightforward task. However, when you have a
heterogeneous environment with different types of equipment having
different types of interfaces the whole management problem begins to get
'messy.' The network manager would like to have one interface converter
type around to use in these situations and use it for whatever type of
conversion is needed. The Model 365 is a neat solution to maintaining
control and avoiding a mess.
The Model 365 allows conversion between EIA-232 and either RS-422 or
RS-485 in just 1 box. The user simply selects either RS-422 or RS-485
for the conversion. Furthermore, the user can select either 2 or 4 wire
RS-485. The universality of this converter goes even further. If RS-485
half duplex is desired for conversion the Model 365 can be configured to
control data flow in either of two ways. It can use RTS of the EIA-232
interface or it can turn on when TD is applied to the EIA-232 interface.
The Model 365 can even give you further flexibility in configuring your
premises data communications network. It may be that you have procured
or inherited all data devices with the same interface and that this
interface is the widespread EIA-232 interface - what else? You put these
inherited devices aside in some storage area. However, some time later
you (and the emphasis is on 'you') decide that you need to interconnect
these types of devices in an RS-485 type 'polling' network. You realize
that your inherited devices do not have the RS-485 interface demanded.
But, you also realize that the Model 365 placed at each of your data
devices gives it an RS-485 interface and allows you to implement the
network you want and without having to go out and buy expensive data
equipment with the needed interface built-in.
This is exactly the situation in the illustration. Here we have a
minicomputer on the left, a plotter in the center and two terminals on
the right. They were all inherited by a laboratory manager in a
well-known company. Each of these devices only came with the EIA-232
interface. After some period of time the laboratory manager decided that
for his installation a network was needed where a minicomputer would
control a plotter and communicate with two terminals and that the
control and communication would be effected by a polling protocol.
RS-485 networking was perfect for this situation. However, the
laboratory manager did not have data devices with the RS-485 interface.
He also did not want 'to bust' his annual budget by going out and
procuring new devices that had this interface. Instead he went to his
storage area and pulled out the inherited devices with the EIA-232
interfaces. He then went and purchased a Model 365 to attach to each
data device and gave it an RS-485 port - an inexpensive solution to his