Methods and apparatus to identify a communication protocol being used in a process control system
Methods and apparatus to identify a communication protocol being used in a process control system are disclosed. An example method includes determining a message structure of a process control message received via a port, determining that the message structure corresponds to a first one of a plurality of process control message protocols, and processing the process control message according to the first process control message protocol.
1. A method, comprising:
detecting, with a logic circuit of a process control device having a first port connected to a first bus and a second port connected to a second bus, a first signal on the first port, the first port corresponding to a first modulation scheme and the second port corresponding to a second modulation scheme;
determining, with the logic circuit, that the first signal received via the first port of the process control device is a first process control message that has a first message structure corresponding to a first process control message protocol of a plurality of process control message protocols;
processing the first process control message according to the first process control message protocol;
after processing the first process control message, determining, with the logic circuit, that a second process control message received via the second port does not conform to the first process control message protocol;
in response to the determining that the second process control message does not conform to the first process control message protocol, determining, with the logic circuit, that the second process control message has a second message structure corresponding to a second process control message protocol different than the first process control message protocol; and
processing the second process control message according to the second process control message protocol.
2. The method of claim 1 , wherein the first process control message protocol corresponds to one of a Highway Addressable Remote Transducer protocol, a MODBUS protocol, or a Bristol Standard Asynchronous Protocol.
3. The method of claim 1 , further comprising:
parsing the first process control message to identify a message field of the first process control message; and
matching content of the message field to a known field of the first message structure corresponding to the first process control message protocol.
4. The method of claim 3 , further comprising determining that the first message structure corresponds to a Highway Addressable Remote Transducer protocol if the content of the message field comprises between five and twenty preamble bytes, each preamble byte including a 0xff symbol when the message field corresponds to a preamble field.
5. The method of claim 3 , further comprising determining that the first message structure corresponds to a Highway Addressable Remote Transducer protocol if the content of the message field comprises a delimiter byte when the message field corresponds to a delimiter field.
6. The method of claim 3 , further comprising determining that the first message structure corresponds to a Highway Addressable Remote Transducer protocol if the content of the message field comprises a five-byte address when the message field corresponds to an address.
7. The method of claim 3 , further comprising determining that the first message structure corresponds to a Highway Addressable Remote Transducer protocol if the content of the message field comprises a command byte when the message field corresponds to a command field.
8. The method of claim 3 , further comprising determining that the first message structure corresponds to a Highway Addressable Remote Transducer protocol if the content of the message field comprises a single checksum byte when the message field corresponds to a checksum field.
9. The method of claim 3 , further comprising determining that the first message structure corresponds to a MODBUS protocol if the content of the message field comprises data associated with a start interval or an end interval when the message field corresponds to the start interval or the end interval.
10. The method of claim 3 , further comprising determining that the first message structure corresponds to a MODBUS protocol if the content of the message field comprises a function byte when the message field corresponds to a function field.
11. The method of claim 3 , further comprising determining that the first message structure corresponds to a Bristol Standard Asynchronous Protocol if the content of the message field comprises seven or twelve header bytes when the message field corresponds to a seven-byte or a twelve-byte header field.
12. The method of claim 3 , further comprising determining that the first message structure corresponds to a Bristol Standard Asynchronous Protocol if the content of the message field comprises a data link escape byte when the message field corresponds to a data link escape field.
13. The method of claim 12 , further comprising determining that the first message structure corresponds to the Bristol Standard Asynchronous Protocol if a second content of a second message field comprises a second data link escape byte when the message field corresponds to a second data link escape field.
14. The method of claim 3 , further comprising determining that the first message structure corresponds to a Bristol Standard Asynchronous Protocol if the content of the message field comprises a start text byte when the message field corresponds to a start text field.
15. The method of claim 3 , further comprising determining that the first message structure corresponds to a Bristol Standard Asynchronous Protocol if the content of the message field comprises an end text byte when the message field corresponds to an end text field.
16. The method of claim 3 , further comprising determining that the first message structure corresponds to one of a MODBUS protocol or a Bristol Standard Asynchronous Protocol if the content of the message field comprises two cyclical redundancy check bytes when the message field corresponds to a two-byte cyclical redundancy check field.
17. The method of claim 1 , wherein the first port is configured to communicate over one of an RS485 bus or a Frequency Shift Keying bus, and the second port is configured to communicate over the other one of the RS485 bus or the Frequency Shift Keying bus.
18. An apparatus comprising:
a first port corresponding to a first modulation scheme;
a second port corresponding to a second modulation scheme different than the first modulation scheme;
a protocol detector to:
detect a first signal on the first port and to determine that the first signal is a first process control message that has a first message structure corresponding to a first process control message protocol of a plurality of possible process control message protocols;
determine that a second process control message received via the second port does not conform to the first process control message protocol; and
in response to the determining that the second process control message does not conform to the first process control message protocol, determine that the second process control message has a second message structure corresponding to a second process control message protocol different than the first process control message protocol; and
a processor to:
process the first process control message according to the first process control message protocol; and
process the second process control message according to the second process control message protocol.
19. The apparatus of claim 18 , wherein the first process control message protocol corresponds to one of a Highway Addressable Remote Transducer protocol, a MODBUS protocol, or a Bristol Standard Asynchronous Protocol.
20. The apparatus of claim 18 , wherein the protocol detector is to determine that the first message structure of the first process control message corresponds to a Highway Addressable Remote Transducer protocol if a content of a message field of the first process control message comprises at least one of:
between five and twenty preamble bytes, each preamble byte including a 0xff symbol, when the message field corresponds to a preamble field,
a delimiter byte when the message field corresponds to a delimiter field,
a five-byte address when the message field corresponds to an address,
a command byte when the message field corresponds to a command field, or
a single checksum byte when the message field corresponds to a checksum field.
21. The apparatus of claim 18 , wherein the protocol detector is to determine that the first message structure of the first process control message corresponds to a MODBUS protocol if a content of a message field of the first process control message comprises at least one of:
data associated with a start interval when the message field corresponds to the start interval,
data associated with an end interval when the message field corresponds to the end interval,
a function byte when the message field corresponds to a function field, or
two cyclical redundancy check bytes when the message field corresponds to a cyclical redundancy check field.
22. The apparatus of claim 18 , wherein the protocol detector is to determine that the first message structure of the first process control message corresponds to a Bristol Standard Asynchronous Protocol if a content of a message field of the first process control message comprises at least one of:
a data link escape byte when the message field corresponds to a data link escape field,
a start text byte when the message field corresponds to a start text field,
seven header bytes when the message field corresponds to a seven-byte header field,
twelve header bytes when the message field corresponds to a twelve-byte header field,
a second data link escape byte when the message field corresponds to a second data link escape field,
an end text byte when the message field corresponds to an end text field, or
two cyclical redundancy check bytes when the message field corresponds to a two-byte cyclical.
23. A tangible machine readable storage medium comprising machine readable instructions, which when executed, cause a machine to at least:
detect that a first signal is received on a first port of a process control device, the first port connected to a first bus and the process control device having a second port connected to a second bus, the first port corresponding to a first modulation scheme and the second port corresponding to a second modulation scheme; determine that the first signal received via the first port of the process control device is a first process control message that has a first message structure corresponding to a first process control message protocol of a plurality of process control message protocols;
process the first process control message according to the first process control message protocol;
after processing the first process control message, determine that a second process control message received via the second port does not conform to the first process control message protocol;
in response to the determining that the second process control message does not conform to the first process control message protocol, determine that the second process control message has a second message structure corresponding to a second process control message protocol different than the first process control message protocol; and
process the second process control message according to the second process control message protocol.
24. A storage medium as defined in claim 23 , wherein the instructions are further to cause the machine to determine that the first message structure corresponds to a Highway Addressable Remote Transducer protocol if a content of a message field of the first process control message comprises at least one of:
between five and twenty preamble bytes, each preamble byte including a 0xff symbol, when the message field corresponds to a preamble field,
a delimiter byte when the message field corresponds to a delimiter field,
a five-byte address when the message field corresponds to an address,
a command byte when the message field corresponds to a command field, or
a single checksum byte when the message field corresponds to a checksum field.
25. A storage medium as defined in claim 23 , wherein the instructions are further to cause the machine to determine that the first message structure corresponds to a MODBUS protocol if a content of a message field of the first process control message comprises at least one of:
data associated with a start interval when the message field corresponds to a start interval,
data associated with an end interval when the message field corresponds to an end interval,
a function byte when the message field corresponds to a function field, or
two cyclical redundancy check bytes when the message field corresponds to a cyclical redundancy check field.
26. A storage medium as defined in claim 23 , wherein the instructions are further to cause the machine to determine that the first message structure corresponds to a Bristol Standard Asynchronous Protocol if a content of a message field of the first process control message comprises at least one of:
a data link escape byte when the message field corresponds to a data link escape field,
a start text byte when the message field corresponds to a start text field,
seven header bytes when the message field corresponds to a seven-byte header field,
twelve header bytes when the message field corresponds to a twelve-byte header field,
a second data link escape byte when the message field corresponds to a second data link escape field,
an end text byte when the message field corresponds to an end text field, or
two cyclical redundancy check bytes when the message field corresponds to a two-byte cyclical.
27. A storage medium as defined in claim 23 , wherein the instructions are further to cause the machine to determine that the first message structure corresponds to one of a MODBUS protocol or a Bristol Standard Asynchronous Protocol if a content of a message field comprises two cyclical redundancy check bytes when the message field corresponds to a two-byte cyclical redundancy check field.