Ascii Query (Read) Example - Johnson Controls FRICK QUANTUM HD Setup

090.040-CS (JAN 14)
Page 48

ASCII Query (Read) Example

To demonstrate how an address within the Quan-
tum™ may be read, the following test can be per-
formed using Windows HyperTerminal (NOTE: Hyper-
terminal cannot be used to test RTU or TCP/IP).
As an example, a MODBUS® command will be cre-
ated and sent to obtain the actual Discharge Pressure
value of a compressor. Using the address tables found
later in this manual, locate the address for Discharge
Pressure. In this case, it is Frick® Address 2003 (dec-
imal). Since this is the only address we are interested
in obtaining the value of, send the following message:
: 01 03 07 D3 00 01 21 CRLF
Where:
Message Start:
Quantum™ ID #:
Read Function:
H. O. address (hex):
L. O. address (hex):
H. O. # of Data Registers:
L. O. # of Data Registers:
Error Correction Code:
Carriage Return - Line Feed:
Look at this message on a more basic level, to un-
derstand how the address that we are requesting is
arrived at. We want to know the actual value of the
Discharge Pressure, Frick® Address 2003 (decimal).
The first part of the message will be a Colon (:). This
represents a heads up alert that data is coming:
: 01 06 1B EE 03 E8 05 CRLF
Where:
Message Start:
Quantum™ ID #:
Write Function:
H. O. address (hex):
L. O. address (hex):
H. O. # of Data Value:
L. O. # of Data Value:
Error Correction Code:
Carriage Return - Line Feed:
Any time that a message is sent, all of the Quantum™
panels on the MODBUS® network will become ac-
tive, communications-wise, once the Colon appears.
Next, the panels will look at the first byte following
the Colon ( : ). If this byte equals the Panel ID # of
the particular Quantum™ being queried, it will imme-
diately finish reading the remainder of the message.
If the byte does not equal its ID #, the message will
be ignored.
QUANTUM™ HD COMPRESSOR CONTROL PANEL
COMMUNICATIONS SETUP
: 01 06 1B EE 03 E8 05 CRLF
Where:
Message Start:
Quantum™ ID #:
Write Function:
H. O. address (hex):
L. O. address (hex):
H. O. # of Data Value:
L. O. # of Data Value:
Error Correction Code:
Carriage Return - Line Feed:
In this particular example, we are strictly looking to
request to view a data value, so we will be perform-
ing a read function (03):
: 01 03 07 D3 00 01 21 CRLF
Where:
Message Start:
Quantum™ ID #:
Read Function:
H. O. address (hex):
L. O. address (hex):
H. O. # of Data Registers:
L. O. # of Data Registers:
Error Correction Code:
Carriage Return - Line Feed:
22003 decimal equals 07D3 hex. Looking at our ex-
ample, we see that we need a H.O. (High Order) ad-
dress and a L.O. (Low Order) address. Since all data
sent and received is in ASCII Hex Byte format, we
need to look at D3 Hex as the Low Order portion of
the address. The High Order portion is 07. Now our
decimal 2003 is formatted as 07D3 Hex.
: 01 03 07 D3 00 01 21 CRLF
Where:
Message Start:
Quantum™ ID #:
Read Function:
H. O. address (hex):
L. O. address (hex):
H. O. # of Data Registers:
L. O. # of Data Registers:
Error Correction Code:
Carriage Return - Line Feed:
Since we are only looking for this one address, and
no other, we can say that we are only looking for
one Data Address. Our Data Address part of the data
packet is also looking for a High and a Low Order
value. Fortunately, the number one (1) is the same in
decimal as it is in Hex, therefore, the Low Order Ad-
dress is 01 (hex). The High Order Address is 00 (hex),