Basler Electric BE1-11 Modbus Protocol - Manual (Page 17)

9424200774 Rev B 11
CRC Error Check
This field contains a 2-byte CRC value for transmission error detection. The master first calculates the
CRC and appends it to the query message. The BE1-11 Protection System recalculates the CRC value
for the received query and performs a comparison to the query CRC value to determine if a transmission
error has occurred. If so, no response message is generated. If no transmission error has occurred, the
slave calculates a new CRC value for the response message and appends it to the message for
transmission.
The CRC calculation is performed using all bytes of the device address, function code, and data block
fields. A 16-bit CRC register is initialized to all 1's. Then each 8-bit byte of the message is used in the
following algorithm:
First, exclusive-OR the message byte with the low-order byte of the CRC register. The result, stored in
the CRC register, will then be right-shifted eight times. The CRC register MSB is zero-filled with each
shift. After each shift, the CRC register LSB is examined. If the LSB is a 1, the CRC register is exclusive-
ORed with the fixed polynomial value A001 (hex) prior to the next shift. Once all bytes of the message
have undergone the above algorithm, the CRC register will contain the message CRC value to be placed
in the error check field.
Reading Fault Record Data
Fault record data is obtained by reading registers from the session fault record. The fault record to be
reported is selected by writing the fault number to register “Fault Report Selection”. See Fault Record
Setup in the Register Table chapter. The selected fault may be from 1 to 255. Entering a value of –1, will
select the most recent fault record.
Contiguous Poll Block Registers
The user may allocate up to 125 holding registers to the Contiguous Poll Block (9875-9999). This
allocation allows dispersed registers that are frequently read to be polled via a single read query. Mapping
can be done via BESTCOMSPlus or via Modbus registers in the Poll Block Settings session. A register is
assigned to a position in the Poll Block by writing its address value into the corresponding position in the
Contiguous Poll Block Assignments registers (9676-9800) in the Poll Block Settings session. Unassigned
position(s) must be mapped to Modbus Dummy Data register (9874), which always returns a value of 0.
Once assignments are made, the values of the assigned registers may be read by polling the Contiguous
Poll Block. For example, if you wanted to continuously monitor VA Primary (10100), IA Primary (10124),
IA Angle (10126), and Total PF (10192) Holding Registers, you would first configure the Contiguous Poll
Block Registers by writing the desired register address values 10100, 10101, 10124, 10125, 10126,
10127, 10192, and 10193 into the Contiguous Poll Block Assignment registers 9676 thru 9683,
respectively. You may now begin monitoring the specified registers by reading the first 8 locations in the
Contiguous Poll Block; ie, reading registers 9875/9876 for VA Primary (as specified in its corresponding
assignment registers 9676/9677), reading registers 9876/9877 for IA Primary (as specified in its
corresponding assignment registers 9678/9679), reading registers 9879/9880 for IA Angle (as specified in
its corresponding assignment registers 9680/9681), and reading registers 9881/9882 for Total PF (as
specified in its corresponding assignment registers 9682/9683).
BE1-11 General Information