Basler DECS-200 - Crc Error Check; Decs-200 Modbus Register Space

DECS-200 Modbus™ Communication 7-9
CRC ERROR CHECK
This field contains a two-byte CRC value for transmission error detection. The master first calculates the
CRC and appends it to the query message. The DECS-200 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 eight-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 a 1, the CRC-register is then
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.
DECS-200 MODBUS REGISTER SPACE
Modbus Address space from 40000 to 49999 refers to Functions Code 3, 6 and 16. The DECS-200 uses
address space from 47001 to 48250 (1250 registers). This address space is divided into 14 areas referred
to as information categories. Table 7-10 provides a statistical summary for each information category.
Table 7-10. Information Category Summary
Information
Category ID
Information
Category
Total # of
Reserved
Holding
Registers
Holding
Register
Address
Space
Number
Of Used
Registers
Access
Right
Data Types
Mapped To
Registers (Total #
Of Variables)
C1
Product
Information
250 47001 to
47250
63 R UCHAR: 63
C2 Metering 125 47251 to
47375
55 R FLOAT: 24
UINT16: 7
C3 Reporting
(Status)
125 47376 to
47500
None R None
(for future use)
C4
Control System
Configuration
Group 1
60
47501 to
47560 59
58 RW
1 R
FLOAT: 26
UINT16: 7
C5
Operating
Modes
60 47561 to
47620
23 16 RW
7 R
UINT16: 23
C6 Setpoints 120 47621 to
47740
94 48 R
46 RW
FLOAT: 45
UINT16: 4
C7 Start-up 60 47741 to
47800
16 RW FLOAT: 8
C8 Limiters 60 47801 to
47860
38 RW FLOAT: 19
C9 Control Loop
Gains
60 47861 to
47920
30 RW FLOAT: 15
C10
Protective
Functions
60 47921 to
47980
37 RW FLOAT: 15
UINT16: 7
C11 Calibration 60
47981 to
48040
None
(for future
use)
RW
None
(for future use)