Frick QUANTUM LX - RTU Query (Read) Example; RTU Response Example

QUANTUM
™
LX EVAPORATOR CONTROL PANEL
COMMUNICATIONS SETUP
090.610-CS (MAY 2016)
Page 43
The next byte tells the Master how many bytes of
information are being returned as a response. In this
case, there are two (2) bytes of valid data.
: 01 03 02 05 D0 25
}
Where:
Message Start:
Quantum™ ID #:
Read Function:
# of Bytes Returned:
Data:
Error Correction Code:
}
The next two bytes (in this case) are the actual data
in response to our original request.
: 01 03 02 05 D0 25
}
Where:
Message Start:
Quantum™ ID #:
Read Function:
# of Bytes Returned:
Data:
Error Correction Code:
}
We need to know what this value means. To break
it down, we must convert the pair of bytes from Hex
to Decimal:
05DO (hex) = 1488 (decimal)
Data to and from the Quantum™ are integer values
with one decimal eld assumed unless shown other-
wise or the command is sent to select two decimal
elds.
From the previous paragraph, we can assume that
there is one decimal place to be applied to the data
value that was returned. Therefore:
1488 (decimal) = 148.8 (decimal)
All temperatures are in degrees C and all pressures
are in PSIA unless the command is sent to select the
units of the panel. Therefore:
148.8 (decimal) = 148.8 PSIA
RTU Query (Read) Example
NOTE: Hyperterminal cannot be used to test
RTU:
In the following example, a MODBUS® command
is sent to obtain the actual Discharge Pressure
value of a compressor. Refer to the following ex-
ample to see what this message packet would
look like:
START ADD. FUNC.
STARTING
ADDRESS
# OF
REGISTERS
TO LOAD
CRC
CHECK
END
T1-T2-T3-T4 01 03 07 D3 00 01 * * T1-T2-T3-T4
* The CRC value is calculated by the trans-
mitting device, which appends the CRC to
the message.
RTU Response Example
Using the RTU Read example just shown, a typi-
cal response would look like:
START ADD. FUNC.
BYTE
COUNT TO
FOLLOW
ANSWER
CRC
CHECK
END
T1-T2-T3-T4 01 03 02 04 23 * * T1-T2-T3-T4
The returned value in the above example is 0423
hex. Converting this to decimal equates to 1059,
and assuming a decimal point gives an answer of
105.9 (PSIA or Panel units, depending on which
has been selected).
End of
message
Start of
message
Quantum™
ID
Function
03 = Read
07 = H. O. Address
D3 = L.O. Address
CRC Error
Correction
Code
00 = H.O. # of Data Registers
01 = L.O. # of Data Registers
End of
message
Start of
message
Quantum™
ID
Function
03 = Read
02 = 2 Bytes
CRC Error
Correction
Code
04 = H.O. Value
23 = L.O. Value