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9. Modbus register map
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9. Modbus register map
A Modbus RTU communication port is integrated for certain
trip unit styles. The trip unit is a server device on the
network and will reply to messages from the client (master).
The trip unit can support a maximum of 122 contiguous
registers (244 data bytes) in a single Modbus transaction.
Table 14. Modbus function codes.
Supported
function codes
Description
2 Read input status
3 or 4 Read holding or input register (interchangeable)
6 Write single register
16 Write multiple registers (contiguous block)
Remember that the registers are numbered starting at 1
but addresses start at 0. In the following sections, register
numbers and addresses (hex) are shown along with their
definition and integer scaling if appropriate. Hex numbers are
shown using the 0x0000 nomenclature.
9.1 Modbus configuration
9.1.1 Network parameters
Modbus connection parameters can be viewed and set from
LCD display, via PXPM and Modbus communication. The
settings are stored beginning at register number 4000. They
may be read by using function code 3 or 4 and written using
function code 6. Note that if you change these settings via
Modbus, they may result in a loss of communication unless
the corresponding change is done by the client.
Table 15. Modbus network parameters.
Function
code
Register
number
Address
(hex)
Definition Data range
3,4,6,16 4000 0x0f9F Address 1 to 247 (factory default
= 1)
3,4,6,16 4001 0x0fa0 Baud rate 0 = 9600 bits/s
1 = 19200 bits/s (factory
default)
2 = 38400 bits/s
3 = 57600 bits/s
3,4,6,16 4002 0x0fa1 Parity 0 = None
1 = Odd
2 = Even (factory default)
3,4,6,16 4003 0x0fa2 Stop bit 0 = 1 bit (factory default)
1 = 2 bits
9.1.2 Exception codes
When there is an error in the request, an exception code will
be returned for the following conditions.
Table 16. Modbus exception codes.
Returned value Condition
0x01 Function or sub-function code in the query is not supported.
0x02 Requested data register/bit address is illegal.
0x03 Data in the query is illegal.
0x04 Trip unit does not support the query function.
0x05 Trip unit received the message and is processing (ACK).
0x06 Trip unit cannot perform the current request at this time
(BUSY).
0x07 Trip unit cannot perform the requested action (NAK).
0x84 A partial register is used in the query.
0x87 Requested event entry does not exist.
9.1.3 Modbus data configuration
The following registers can be written to configure the trip
unit response. They may also be read for verification.
Table 17. Modbus data configuration.
Function
code
Register
number
Address
(hex)
Register definition
3,4,6,16 2001 0x07D0 Invalid object access
configuration:
If = Non-zero (default), any attempt to
access a group of data objects that
contain an invalid object will result in
the 0x02 illegal data code.
If = 0, the trip unit will respond with
valid data in the valid objects and
0x0000 for invalid objects
3,4,6,16 2002 0x07D1 Floating point data word
order configuration:
If = Non-zero (default), the floating-
point low order word is first.
If = 0, the floating-point high order
word is first.
3,4,6,16 2003 0x07D2 32-bit fixed-point data word
order configuration:
If = Non-zero (default), the fixed-point
low order word is first.
If = 0, the fixed-point high order word
is first.
9.1.4 Diagnostics
The trip unit supports internal Modbus diagnostics to
monitor port communication using function code 08 accord-
ing to Table 17.
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