Instructions

Frame Objects 80
Doc: HMSI-27-314, Rev. 3.10Anybus Communicator EtherNet/IP / Modbus-TCP User Manual
14.7 Checksum Object
Most serial protocols features some way of verifying that the data has not been corrupted during trans-
fer. The Checksum Object calculates and includes a checksum in a transaction.
Parameter Description
Error Check Start byte
Specifies the byte offset in the transaction to start checksum calculations on.
a
a. In Generic Data Mode the Start character (if used) will not be included in the checksum calculation.
Error Check Type This parameter specifies which type of algorithm to use:
• CRC (2 bytes)
CRC-16 with 0xA001 polynome (Modbus RTU standard)
•LRC (1 byte)
All bytes are added together as unsigned 8-bit values. The two’s complement of the result
will be used as a checksum.
(Modbus ASCII standard with Error Check Start Byte = 0x01 and Representation = ASCII)
• XOR (1 byte)
All bytes are logically XOR:ed together. The resulting byte will be used as a checksum.
• ADD (1 byte)
All bytes are added together as unsigned 16-bit values. The lowest 8 bits in the result will
be used as a checksum.
Error check type
combined with
The binary value can be converted to its one’s or two’s complement. This conversion is carried
out before ASCII formatting (see next parameter).
• None
The checksum binary value is transmitted without conversion.
• One’s complement
The checksum value will be converted to its one’s complement (inverse code).
Example: 00001100 will be transmitted as 11110011
• Two’s complement
The checksum value will be converted to its two’s complement (complement code).
Example: 00001100 will be transmitted as 11110100
Representation •Binary
The checksum is transmitted in binary format.
•ASCII
All characters in the checksum are converted to ASCII values.