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QUANTUM™ LX COMPRESSOR CONTROL PANEL
COMMUNICATIONS SETUP
090.020-CS (JUNE 11)
Page 35
SECTION 3
QUANTUM™ LX ALLEN-BRADLEY COMMUNICATION
QUANTUM™ LX ALLEN-BRADLEY COMMUNICA-
TION
This section contains programming examples for
reading data from and writing data to the Frick Quan-
tum control panel from an Allen Bradley (AB) SLC500
or PLC5 processor. Allen Bradley (AB) RSLogix500
programming software has been used for the follow-
ing examples, however, these examples can also be
used for the AB RSLogix5 software.
Overview Of Half And Full Duplex Theory
To provide for the reading and writing of data
to Quantum™ LX panels using Allen-Bradley
communication, the Quantum™ LX has an Allen-
Bradley DF1 communication driver that recog-
nizes either half or full duplex SLC 500 protected
typed logical read and write commands (either
half or full duplex must be selected). Half-duplex
simply means that data can only be sent in one
direction at a time (the concept of how a walk-
ie-talkie works). Using full-duplex, data can be
sent and received simultaneously (the concept of
how a telephone works). This is a
Leader
/
Follower
multi-drop communication method.
The Quantum™ LX talks Allen-Bradley SLC pro-
tocol and is programmed to resemble an Allen-
Bradley SLC500
follower
station. The customer’s
PLC or DCS must be setup to initiate the read-ing
and writing of data to a Quantum™ LX. The
Quantum™ LX does not initiate any communica-
tions. The panel ID number is used as its sta-
tion address and the target node. With the AB
PLC, the MSG (Message) instruction is used to
send read and write requests. A DCS (Distributed
Control System) will use a SLC 500 DF1 protocol
driver to send protected typed logical read with
3 address
fi
elds and protected typed logical write
requests with 3 address
fi
elds to a Quantum™
LX.
Fifty (50) data elements can be read with one
read.
Setpoints are changed by sending a write com-
mand to one element. Changing a setpoint
causes the Quantum™ LX to save the new set-
point to Flash memory (non-volatile memory).
Be careful not to continuously request a set-
point change. It is to be expected that com-
munications may slow down during the pro-
cess of writing setpoints or clearing alarms.
Both of these processes involve writing to ei-
ther EEPROM or Flash Memory and does take
some time. If communication requests are
being sent faster than once every couple of
seconds, there will be temporary slowdowns
during these processes.
Additionally, keeping the Quantum™ LX busy
writing to Flash memory will interfere with the
communications to its I/O Boards. A communi-
cation failure to an I/O board will cause the com-
pressor to shutdown. Control commands such
as starting the compressor are also sent with a
write command. For more detail and a list of the
data, reference the Quantum™ LX Data Table
section. For details about the actual protocol,
reference the AB publication 1770-6.5.16
DF1
Protocol and Command Set Reference Manual
.
Because overrun can occur, the baud rate and
commands should be setup to produce the
most desired throughput. The
leader
station
should have the Stop Bit and Parity set to
match the Quantum™ LX, Duplicate Detect
disabled, and Error Detect set for BCC or CRC.
When communication is between either your
programming software and a Quantum™ LX or
an Allen-Bradley PLC and a Quantum™ LX on
a multi-drop link, the devices depend on a
DF1
Leader
to give each of them polling
permission to transmit in a timely manner. As
the number of Quantum™ LX
followers
increase on the link, the time between when
each panel is polled also increases. This
increase in time may become larger if you
are using low baud rates. As these time
periods grow, the timeouts such as the
message timeout, poll timeout and reply
timeout may need to be changed to avoid loss
of com-munication.
ACK Timeout
- The amount of time in 20
milli-seconds increments that you want the
processor to wait for an acknowledgment to
the message it has sent before the processor
retries the mes-sage or the message errors out.
Reply Message Wait Time
- De
fi
ne the
amount of time in 20 millisecond increments
that the
leader
station will wait after receiving
an ACK (to a
leader
-initiate message) before
polling the remote station for a reply. Choose a
time that is, at minimum, equal to the longest
time that a remote station needs to format a
reply packet. Some remote stations can format
reply packets faster than others.
Message Timeout
- De
fi
nes the amount of
time in seconds that the message will wait for a
reply.
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