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Unit
LS 4 #6
LS 4 #7
LS 4 #8
Table 6.2: Modbus slave ID relationship
A standard LS 4 occupies only the range from 3:0001 to 3:0029. The remaining range is
reserved for future expansion of the LS 4 or custom versions.
If no response was obtained from the target GCP-30 unit, Modbus exception code
0B Gateway target device failed to respond is returned.
The following table lists the Modbus exception responses sent by the gateway instead
of a normal response message in case of an error:
Modbus exception
code
01
02
03
0B
Table 6.3: Modbus exception codes
Alternative access of Input Registers as Holding Registers
Since firmware version 1.3 the Input registers located in the 3:0001 and 3:1001 range
can alternatively be accessed as Holding registers in the range 4:0101 and 4:1001
respectively.
GCP-30 MUX data table 3:0001
The GCP-30 MUX data table contains all data values a GCP-30 is transmitting cyclically
on the CAN bus. A GCP-30 sends a value every 100 ms. Therefore it takes approximately
between 2.3 and 3 seconds for a complete update of the data table with new values from
the CAN bus. The data table can be polled much faster by a Modbus master, however
faster poll rates would not offer higher update cycles.
The GCP-30 MUX data table is located in the so called Input register address block, which
sometimes is also identified with offset 3:0000.
function code 04 Read input registers.
1
Alternative access as "Holding Registers" is possible at 4:0101 since firmware 1.3
34
Modbus
Modbus read
slave ID
address range
22
3:0001-3:0100
23
3:0001-3:0100
24
3:0001-3:0100
Exception name
Illegal function
Illegal data address
Illegal value
Gateway target device
failed to respond
Modbus write
address range
4:0003
4:0003
4:0003
Reason
A Modbus master sent a Modbus function which is not supported by the
gateway. Please refer to the documentation of the individual data tables
for valid function codes.
A Modbus master queried a non-existing Modbus address or the queried
range points outside of a data table. Please refer to the documentation of
the individual data tables for valid address ranges.
A Modbus master sent a Modbus message which's structure or implied
length is invalid. Also returned if a Modbus master tries to access remote
control functions for a unit configured as read-only.
A Modbus master tries to access data which is unavailable because no re-
sponse was obtained from the target GCP-30 or LS 4 unit. Usually means
that the unit is not present on the CAN bus.
1
The block is accessed using Modbus
Modbus floating point
address range
3:1001-3:1034
3:1001-3:1034
3:1001-3:1034
UMGCPMG-2201
CAN ID
822
823
824
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