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9440300990 Rev J
Modbus™ Communication
DECS-250
Example: If the above string is changed to “P”, the new string will read as follows:
Holding Register
Value
K (Hi Byte)
‘P’
K (Lo Byte)
hex 00
K+1 (Hi Byte)
hex 00
K+1 (Lo Byte)
hex 00
K+2 (Hi Byte)
hex 00
K+2 (Lo Byte)
hex 00
K+3 (Hi Byte)
hex 00
K+3 (Lo Byte)
hex 00
The same byte alignments are required to write.
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-250 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 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 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.
Secure DECS-250 Login via Modbus
To login to the DECS-250 via Modbus, write the string
username
|
password
to the Secure Login register
(40500). Substitute “username” with the user name of the desired access level, include the pipe “|”
symbol, and substitute “password” with the password of the chosen access level. To view the current
access level, read the Current Access register (40520). Write any value to the Logout register (40517) to
log out of the DECS-250. Upon disconnecting from Modbus over TCP/IP, the user is automatically logged
out of the DECS-250. However, upon disconnecting from Modbus over serial line, the user remains
logged in.
Modbus Parameters
General
General parameters are listed in Table 23.
Table 23. General Group Parameters
Group
Name
Register
Type
Bytes
R/W
Range
System Data
Model Number
40001
String
64
R
0 - 64
System Data
App Version Information
40033
String
64
R
0 - 64
System Data
App Sub-version Version
40065
String
64
R
0 - 64
System Data
Boot Version Information
40097
String
64
R
0 - 64
System Data
Firmware Part Number
40129
String
64
R
0 - 64
Time
Date
40161
String
16
R
0 - 16
Time
Time
40169
String
16
R
0 - 16
Unit Information
Style Number
40177
String
32
R
0 - 32
Summary of Contents for DECS-250
Page 2: ......
Page 6: ...iv 9440300990 Rev J Revision History DECS 250 ...
Page 16: ...xiv 9440300990 Rev J Contents DECS 250 ...
Page 20: ...4 9440300990 Rev J Introduction DECS 250 ...
Page 28: ...12 9440300990 Rev J Power Stage DECS 250 ...
Page 32: ...16 9440300990 Rev J Voltage and Current Sensing DECS 250 ...
Page 40: ...24 9440300990 Rev J Synchronizer DECS 250 ...
Page 52: ...36 9440300990 Rev J Auxiliary Control DECS 250 ...
Page 56: ...40 9440300990 Rev J Contact Inputs and Outputs DECS 250 ...
Page 84: ...68 9440300990 Rev J Limiters DECS 250 ...
Page 114: ...98 9440300990 Rev J Power System Stabilizer DECS 250 Figure 96 PSS Parameter Settings ...
Page 124: ...108 9440300990 Rev J Stability Tuning DECS 250 ...
Page 126: ...110 9440300990 Rev J Mounting DECS 250 Figure 103 Overall and Projection Mounting Dimensions ...
Page 127: ...9440300990 Rev J 111 DECS 250 Mounting Figure 104 DECS 250 Escutcheon Plate Dimensions ...
Page 198: ...182 9440300990 Rev J Timekeeping DECS 250 ...
Page 210: ...194 9440300990 Rev J CAN Communication DECS 250 ...
Page 304: ...288 9440300990 Rev J Maintenance DECS 250 ...
Page 316: ...300 9440300990 Rev J Specifications DECS 250 ...
Page 334: ...318 9440300990 Rev J Analog Expansion Module DECS 250 ...
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