S90-010 CS (APR 08) FRICK
®
QUANTUM™ COMPRESSOR CONTROL PANEL
Page 24 COMMUNICATIONS SETUP
ALLEN-BRADLEY COMMUNICATION
To provide for the reading and writing of data to
Quantum™ panels using Allen-Bradley communication,
the Quantum™ has an Allen-Bradley DF1 communication
driver that recognizes both half-duplex and full duplex SLC
500 protected typed logical read and write commands.
This is a Master / Slave multi-drop communication
method. The Quantum™ talks Allen-Bradley SLC protocol
and is programmed to resemble an Allen-Bradley SLC500
slave station. The customer’s PLC or DCS must be setup
to initiate the reading and writing of data to a Quantum™.
The Quantum™ does not initiate any communications.
The Quantum™ panels ID number is used as its station
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 fields and protected typed
logical write requests with 3 address fields to a
Quantum™. Fifty (50) data elements can be read with one
read. The most desired data (information on the
Operating
Status
screen) exists in a fifty (50) element data area.
Setpoints are changed by sending a write command to
one element. Changing a setpoint causes the Quantum™
to save the new setpoint to Flash memory (non-volatile
memory).
Be careful not to continuously request a
setpoint change. It is to be expected that
communications may slow down during the process
of writing setpoints or clearing alarms. Both of these
processes involve writing to either 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™
busy writing to Flash memory will interfere with the
Quantum™ communicating to it’s I/O Boards. A
communication failure to an I/O board will cause the
compressor 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™ 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 master station should have the Stop Bit set to 1,
Parity set to none, Duplicate Detect disabled, and Error
Detect set for BCC or CRC.
When communication is between either your programming
software and a Quantum™ or an Allen-Bradley PLC and a
Quantum™ on a multi-drop link, the devices depend on a
DF1 Master to give each of them polling permission to
transmit in a timely manner. As the number of Quantum™
slaves increase on the link, the time between when each
Quantum™ 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 communication.
ACK Timeout
- The amount of time in 20 milliseconds
increments that you want the processor to wait for an
acknowledgment to the message it has sent before the
processor retries the message or the message errors out.
Reply Message Wait Time
- Define the amount of time in
20 millisecond increments that the master station will wait
after receiving an ACK (to a master-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
- Defines the amount of time in
seconds that the message will wait for a reply. If this time
elapses without a reply, the error bit is set, indicating that
the instruction timed out. A timeout of 0 seconds means
that there is no timer and the message will wait indefinitely
for a reply. Valid range 0-255 seconds.
Note: Make sure the Allen-Bradley PLC and the
programming software is the most recent software
revision. Some revisions have been made that do not
allow the SLC Typed Logical Read/Write Message
Command.
SLC-500 - Suggested Setup
Channel Configuration
Configure the communication channel – Channel 0:
Current Communication Mode: System
Communication Driver: DF1 Half-Duplex Master or DF1
Full-Duplex
Baud Rate: 19200 (suggested)
Stop Bits: 1
Duplicate Detect: Disabled
ACK Timeout (x20ms): 30
Message Retries: 3
Parity: None
Station Address (Source ID): 5 (Master’s DF1 selected
ID#)
Error Detect: BCC / CRC
RTS off Delay (x20ms): 0
RTS Send Delay (x20ms): 0
Pre-Send Time Delay (x1 ms): 0
Control Line: No Handshaking
Polling Mode: Message Based (do not allow slave to
initiate messages)
Priority Polling Range - Low: 255, High: 0
Normal Polling Range - Low: 255, High: 0
Normal Poll Group Size: 0
Reply Message Wait Time (x20ms): 20
System Mode Driver: DF1 Half-Duplex Master or DF1 Full-
Duplex
User Mode Driver: Generic ASCII
Write Protect: DISABLED
Mode Changes: DISABLED
Mode Attention Character: \0x1b (default)
System Mode Character: S (default)
User Mode Character: U (default)
Edit Resource/File Owner Timeout (Sec): 60
Passthru Link ID (decimal): 1
