11
FUNCTION
SUB FUNCTION
HEX
DESCRIPTION
DEC
HEX
DEC
17
11
Diagnostic
– Return follower busy count
18
12
Diagnostic
– Return bus character overrun count
20
14
Diagnostic
– Clear overrun counter and flag
11
0B
Get communication event counter
12
0C
Get communication event log
15
0F
Write multiple coils
16
10
Write multiple registers
17
11
Report follower ID
22
Mask write register
23
17
Write multiple registers
24
Read FIFO Queue
Table 7
– Modbus function set
E. MODBUS EXCEPTION CODES
CODE
NAME
MEANING
01
ILLEGAL FUNCTION
This code is received when an illegal action is entered into the building management
system. This may be because the function code is only applicable to newer devices,
or the follower device is in the wrong state to process a request of this type.
02
ILLEGAL DATA ADDRESS
This code is received when an illegal data address is entered into the building
management system. More specifically, the combination of reference number and
transfer length is invalid.
03
ILLEGAL DATA VALUE
This code indicates that an illegal value has been entered into the building
management system.
04
FOLLOWER DEVICE FAILURE
An error occurred while the follower was attempting to perform the requested action.
05
ACKNOWLEDGE
Indicates that the server (or follower) has accepted the request, but will take a
significant amount of time to process it. This response prevents a timeout error.
06
FOLLOWER DEVICE BUSY
This is received when a follower device is busy processing a programmed command.
User should query this device at a later time.
08
MEMORY PARITY ERROR
The server (or follower) attempted to read a file, but detected a parity error in the
memory. The user can retry the request, but service may be necessary to fix this
error.
0A
GATEWAY PATH UNAVAILABLE
Indicates that the gateway was unable to allocate an internal communication path
from the input port to the output port.
0B
GATEWAY TARGET DEVICE
FAILED TO RESPOND
Specialized use in conjunction with gateways - indicates that no response was
obtained from the target device. Usually means that the device is not present on the
network.
Table 8
– Modbus exception codes
PART 6 - REGISTER MAP
A. PRIMARY DATA TABLES
TABLE
DATA TYPE
READ/WRITE
DESCRIPTION
Discrete Inputs
Single bit
Read only
Data can be provided by an I/O system.
Coils
Single bit
Read / Write
Data can be altered by an application program.
Input Registers
16-bit word
Read only
Data can be provided by an I/O system.
Holding Registers
16-bit word
Read / Write
Data can be altered by an application program.
Table 9
– Supplementary information
B. APPLIANCE MEMORY MAP
ADDRESS
DESCRIPTION
DEFAULT
UNIT
MIN
MAX
RESOLUTION
COILS
00001
Appliance enable / Room
thermostat / Stage 1
0
1 = on, 0 = off
0
1
1
00005
Tank thermostat
0
1 = on, 0 = off
0
1
1
00006