Operation manual
13
EWWP014~065KBW1N
Packaged water-cooled water chillers
4PW61660-1A – 04.2012
Data representation of the Modbus protocol
■
Digital
All digital data is coded by a single bit:
■
"0" for OFF
■
"1" for ON.
All digital variables are assigned to bits of consecutive registers,
each one having:
■
the lower-address variable assigned to the less significant bit
■
the higher-address variable assigned to the most significant
bit.
■
Analogue and integer data
An analogue and integer value is represented by a 16-bit WORD
register in binary notation. For each register, the first byte
contains the high order bits and the second byte contains the
low order bits.
■
The analogue variables are represented in tenths:
for example, the value 10.0 is transmitted as 0064h=100d
for example, the value –10.0 is transmitted as FF9Ch=–100d
■
The integer variables are transferred using the effective
value:
for example, the value 100 is transmitted as 0064h=100d
The address card operates on registers where one register must
be considered at 16-bit.
In case the BMS or supervisory system tries to write a value of a
parameter that is out of range, the writing will be ignored.
Implemented error code
Defining the BMS setting
Activating the Modbus protocol
The Modbus protocol is activated by setting the
h23
parameter to
1
.
This is a user parameter, refer to
"How to consult and modify the user
parameters" on page 10
.
Defining the unit's serial address
To define each unit's unique serial address required for
communication with the supervisionary system, set parameter
h10
.
This is a user parameter, refer to
"How to consult and modify the user
parameters" on page 10
.
Variables database
The BMS or supervisory system and the chiller unit communicate
through a fixed set of variables, also called address numbers.
Hereafter, you will find the information you need about the digital,
integer and analogue variables that the BMS or supervisory system
can read from or write to the address card of the chiller.
For addresses of all the direct and user parameters refer to
"Overview of the direct and user parameters" on page 9
.
Overview of all variables which are not direct or user
parameters
Code
Modbus interpretation
Condition
1
Illegal function
Message is not supported or the
number of variables required is greater
than the allowed limit (length
≤
20)
Description
Modbus
address
Parameter
type
(a)
(a) D=digital.
Circuit alarm
1=A1, HP1, or LP1
alarm codes active
0=no alarm code active
Read
only
41
D
General alarm
1=FL alarm code
0=no alarm code active
Read
only
45
D
NTC Probe alarm
1=E1, E2, or E3 alarm
codes
0=no alarm code active
Read
only
46
D
Input of flowswitch
alarm
1=closed
0=open
Read
only
53
D
Input of
changeable digital
S7S input
1=closed
0=open
Read
only
54
D
Input of high
pressure or
discharge protector
or overcurrent
alarm
1=closed
0=open
Read
only
55
D
Input of low
pressure switch
alarm
1=closed
0=open
Read
only
56
D
Input of
changeable digital
S9S input
1=closed
0=open
Read
only
57
D
Output of
compressor 1
1=on
0=off
Read
only
59
D
Output of
compressor 2
1=on
0=off
Read
only
60
D
Output of pump
1=on
0=off
Read
only
61
D
Output of reversing
valve
1=on
0=off
Read
only
62
D
Output of alarm
1=on
0=off
Read
only
63
D
On or off
1=on
0=off
Read/
write
64
D
Cooling or heating
1=cooling
0=heating
Read/
write
65
D