TPU2000/2000R Modbus/Modbus Plus Automation Guide
247
6. (If the LSB was 1): Exclusive OR the CRC register with the polynomial value
A001 hex (1010 0000 0000 0001)
7. Repeat Steps 3 and 4 until 8 shifts have been performed. When this is done, a
complete 8-bit byte will have been processed
8. Repeat Steps 2 through 5 for the next 8 bit byte of the message. Continue
doing this until all bytes have been processed.
9. The final contents of this CRC register is the CRC value.
10. When the CRC is placed into the message, its upper and lower bytes must be
swapped as described below.”
The CRC- 16 message generation capability is best done by a hardware chip or using a software algorithm.
Within the aforementioned manual, the protocol’s inventor supplies a C language program to calculate the CRC-
16 code. It is advised that the text be referenced for those wishing to calculate such a code.
TPU2000/TPU2000R Modbus Exception Response Analysis
If the TPU2000/TPU2000R does not understand the command sent to the device or if the command is sent in the
wrong format, the TPU2000/TPU2000R shall generate an exception response. A Modbus exception response is
in the format of that shown in Figure 5-73. As illustrated, the function code is “ANDed” with 80 HEX. Following
the modified function code, an exception code byte will follow. The customary LRC and terminator of a Carriage
Return and Line feed will terminate the communication string.
Table 5-83 shall list the standard Modbus Exception Codes and Table 5-84 lists the exception codes as the
TPU2000/TPU2000R reports them. Notice that the TPU2000/TPU2000R does not report its exception codes as
per the Modbus standard defined codes.
Table 5-83. Modbus Standard Exception Codes
Code Name
01 ILLEGAL FUNCTION
02 ILLEGAL DATA ADDRESS
03 ILLEGAL DATA VALUE
05
CKNOWLEDGE
06 SLAVE DEVICE BUSY
07 NEGATIVE ACKNOWLEDGE
08 MEMORY PARITY ERROR
Table 5-84. TPU2000/TPU2000R Defined Exception Codes
Code Description
01 INVALID PASSWORD
04 INVALID REGISTER ADDRESS
05 INVALID RANGE ACCESSED
06 INVALID DATA
34 INVALID FUNCTION CODE
36 SUPERVISORY CONTROL DISABLED
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