S90-510 CS (MAR 07)
FRICK
®
QUANTUM™ LX AcuAir
®
CONTROL PANEL
Page 6
COMMUNICATIONS SETUP
RS-232 DESCRIPTION
RS-232 is by far the most common (and oldest)
communications hardware protocol, as almost all
laptop and desktop computers will have at least one
RS-232 serial communications port available. It was
initially developed for the emerging computer industry
in the 1960’s. Originally, it was a method of sending
data from a mini or main frame computer, to devices
such as printers, punch card readers, teletypes,
magnetic tape units and modems. In those early days,
the maximum speed at which RS-232 was capable of
transmitting (about 9600 bits per second), was quite
satisfactory, as most of the receiving devices were
mechanical in nature (except for modems), and barely
able to keep up with these speeds.
RS-232 uses single ended TX (transmit data) and RX
(receive data). This means a common ground wire is
shared between TX and RX, so only 3 wires are
needed or a data only serial channel: TX, RX, and
GND.
Disadvantages of single ended signaling is that it is
more susceptible to noise than differential signaling
(RS-422/485), effective cable distances are shorter
(typically about 50 Ft. total, due to low noise
immunity) and data rates are slower. Additionally,
there is the limitation that only two devices can
communicate together (
leader
and
follower
).
The Quantum™ controller has two RS-232 ports
available. One of these is TB2 (Com-2), the other is
PL6 (Com-3). Both TB2 (Com-2) and PL6 (Com-3)
may be used concurrently.
RS-232 signals cannot be connected directly to either
an RS-422 or RS-485 device. These signals must first
be conditioned (converted). See the section entitled
Converting an RS-232 Signal to RS-422/485 for
details.
RS-422/RS-485 DESCRIPTION
When serial communications started moving into the
industrial environment, it was quickly noted that
because of the high electrical noise potential from
electric motors, valves, solenoids, fluorescent lighting,
etc., that the noise immunity characteristics of RS-232
protocol was grossly lacking. Additionally, the
distances between the communicating equipment on
the factory floor was much greater than that within the
typical office environment. For these reasons, RS-422
and RS-485 was developed.
•
RS-422 is a full duplex communications
hardware protocol. This means that it data
can be sent and received simultaneously.
Frick® Controls uses a 4-wire system for
RS-422 (two transmit wires and two receive
wires). Advantages of RS-422 over RS-232
is that up to 30 Quantum™ controllers may
be simultaneously connected using a daisy-
chain wiring scheme (to be explained later),
and that the distances involved can be much
greater (typically up to 2000 ft. for the total
cable run), much greater noise immunity
than RS-232.
•
RS-485 is a half duplex bus. This means that
it can only send or receive data at any given
time. It cannot do both at the same time.
Frick
®
Controls uses a 2-wire system for RS-
485 (one positive transmit / receive wire and
one negative transmit / receive wire). Up to
30 Quantum™ controllers may be
simultaneously connected up to a total
distance of 2000 ft. using a daisy-chain
wiring scheme (to be explained later). One
advantage to using RS-485 as opposed to
RS-422 is that only a single twisted pair
cable need to be run to all devices (while
RS-422 requires a double twisted pair
cable). Additionally, the RS-485 and RS-422
protocols have much greater noise immunity
than RS-232.
RS-422/RS-485 signals cannot be connected directly
to an RS-232 device. These signals must first be
conditioned (converted). See the section entitled
Converting an RS-232 Signal to RS-422/485 for
details.