QUANTUM
™
LX EVAPORATOR CONTROL PANEL
COMMUNICATIONS SETUP
090.610-CS (MAY 2016)
Page 13
SECTION 2
SERIAL COMMUNICATIONS
SERIAL COMMUNICATIONS DESCRIPTION
RS-232 DESCRIPTION
NOTE: The Q5 board does not utilize RS-232.
Almost all laptop and desktop computers have
at least one RS-232 serial communications port
available. It was initially developed for the emerg-
ing 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 transmit-
ting (about 9600 bits per second), was quite sat-
isfactory, 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 for a data only serial channel: TX, RX,
and GND.
Disadvantages of single ended signaling is that it
is more susceptible to noise than differential sig-
naling (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 (master and slave).
RS-422/RS-485 DESCRIPTION
When serial communications started moving into the
industrial environment, it was quickly noted that be-
cause of the high electrical noise potential from elec-
tric motors, valves, solenoids, uorescent lighting, etc.,
that the noise immunity characteristics of RS-232 pro-
tocol was grossly lacking. Additionally, the distances
between the communicating equipment on the factory
oor was much greater than that within the typical of-
ce 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 data, or receive data at any given time.
It cannot do both at the same time. Frick® Con-
trols 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 ca-
ble), much greater noise immunity than RS-232.
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