42
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COMMUNICATIONS
The protocol to be used is Modbus RTU. This is implemented by the master (PC, PLC, etc.) issuing a
poll to the slave (BurnerLogix) and the slave responding with the appropriate message.
A typical format of a poll request is as follows:
MESSAGE FORMAT
DST refers to the logical address of the slave.
FNC is the function being requested. FNC 03 is a read request.
ADR is the message number or register number of the data being requested.
For the BurnerLogix all registers are mapped as HOLDING REGISTERS, FNC 03. Register
addresses begin at 40001 but is interpreted as address 00.
DAT is the number of words being requested. A word is an integer consisting of 2 bytes.
The normal response from a slave is as follows:
DBC is the data byte count being returned. It must be two times the DAT number from the poll
request.
DATA is the data returned and is always a series of 2 byte integers. If 4 words were requested then
DBC would be 8 and there would be 8 data bytes or 4 data words containing the requested data.
The format of the data is N,8,1 meaning no parity, and 1 stop bit. Baud rate is selectable
through the keypad / display. As shipped the baud rate is 9600.
Communication to the BurnerLogix control is made through
either of the RJ-12 jacks located on the underside of the control
(note figure on right). The jacks are internally wired in parallel to
ease multi-dropping of BurnerLogix controls. For each of the RJ-
12 connections, the outside contacts are connected together and
are designated as “A” or “+” while the inside contacts are con-
nected together and are designated as “B” or “-”. Fireye supplies
the ED512 cables in various lengths with RJ-12 plugs on each
end. Refer to bulletin E-8002 for additional information.
See page 43 for a table of currently available messages provided by the BurnerLogix programmers,
followed by a description where necessary
DST
FNC
ADR
HI
ADR
LO
DAT
HI
DAT
LO
CRC
LO
CRC
HI
DST
FNC
DBC
DATA….
Hi/Lo
CRC
LO
CRC
HI
COMMS
COMMS
EXP
EXP
RUN/CHK
RUN/CHK