Bently Nevada 3300/01 Series, Operation Manual, Page: 47 / 78

System Monitor
Data Type
Rack Starting Address
DIRECT VALUES
MONITOR STATUS
0
0
80175-01
16 PROTOCOL SPECIFICATIONS
MODBUS PROTOCOL DATA ADDRESSING
The Serial Interface uses fixed protocol addresses for the starting locations of rack data. These
addresses are n o t the physical addresses o f the data in the interface memory. They are the
addresses used in the protocol messages to access data which is available from the interface. The
starting addresses for Modbus protocol are
Note
For addressing purposes, a 2 channel double-wide monitor looks like a 2 channel single-
wide monitor in the left slot followed by a empty right slot. A single channel monitor will
be treated as a dual channel monitor with an invalid data value for channel 2.
DIRECT VALUES
Direct values occupy contiguous protocol addresses. The starting address for the direct values
is address 0. This is the address of the first direct value of the first monitor location in the rack.
The first monitor (slot 1) is the left most monitor just to the right of the System Monitor. The entire
rack's direct values are found sequentially in adjacent addresses. Each monitor will have two direct
values associated with it unless it is a 6-channel monitor. In that case, it will have 6 direct values.
The presence of 6-channel monitors will be indicated by the SW3 switch on the Serial Interface
circuit board. Channel direct values a r e ordered first channel t o l a s t channel. O n c e t h e
configuration of the rack is known, then the exact locations of all the rack's direct values can be
specified. A simple formula which can be used to calculate the starting address of any monitor's
direct values is:
Starting address = 2(monitor slot number - 1) + 2(number of 6-channel monitors to left of the
selected monitor)
Use the Read Input Registers command (Function Code 4) t o access the direct values for the
rack.
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