Basler Electric DECS-250N - Manual (Page 224)

208 9440500990 Rev D
Modbus™ Communication DECS-250N
K+3 (Lo Byte) ‘D’
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-250N 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 e 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.
Secure DECS-250N Login via Modbus
To login to the DECS-250N 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 “|”
character, 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-250N. Upon disconnecting from Modbus over TCP/IP, the user is automatically
logged out of the DECS-250N. However, upon disconnecting from Modbus over serial line, the user
remains logged in.
Modbus Parameters
General
General parameters are listed in Table 24.
Table 24. 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