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Issue/Rev. 0.1 (9/13) ║ MNFL003 • Page 35
microFlow.net Liquid Modbus Communications Manual
Appendix
Query
Field Name
Example (Hex)
microFlow.net Liquid Address
11
Function
10
Starting Address Hi
00
Starting Address Lo
01
No. of Registers Hi
00
No. of Registers Lo
02
Byte Count
04
Data Hi
00
Data Lo
0A
Data Hi
01
Data Lo
02
Error Check (CRC)
--
Response
A normal response consists of the slave address, function code, starting address, and
quantity of registerspreset.
An example of a response to the preceding query appears below:
Response
Field Name
Example (Hex)
microFlow.net Liquid Address
11
Function
10
Starting Address Hi
00
Starting Address Lo
01
No. of Registers Hi
00
No. of Registers Lo
02
Error Check (CRC)
--
5.5
Exception Responses
When a master device sends a query to an microFlow.net Liquid device, there are three
possible outcomes:
1. The microFlow.net Liquid receives the query with no communication errors,
handles the query normally, and returns a normal response.
2. A communication error bars the microFlow.net Liquid from receiving the query,
so no response is returned. The master program eventually processes a timeout
condition for the query.
3. The microFlow.net Liquid receives the query without error, but returns no
response. The master program eventually processes a timeout condition for the
query.
Two fields in the exception response message differentiate it from a normal response:
Function Code Field:
A microFlow.net Liquid normally echoes the function code of
the original query in the function code field of the response. Because the values of all
function codes are below 80 hexadecimal, all function codes have a most significant bit
(MSB) of 0. In an exception response, however, the slave sets the MSB of the function
code to 1. The value of the function code in an exception response is therefore 0x80
(hex) higher than the value for a normal response.