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11.4.0 Modbus Protocol Support
11.4.1 Modbus Commands
The T-3 card supports a command subset of the Modbus Specification consisting
primarily of the Function Codes required to read and write data. The following sections
detail the different commands supported by the card.
Function Address Slave Driver
Code Command Range Comments
2 Read Input Status 10001 Module returns binary data from the
to “Input Status” register space.
10331 & 10833
3 Read Multiple 40001 The Module returns word data from
Registers to the register space. The module will
40138 support up to 125 words of data in
one command.
4 Read Input Registers 30001 The module returns data from the
to “Input register” space in the module.
30138 The module will support up to 125
words of data in one command.
6 Single Register Write 40001 to 40030 This is a register write command
and allowing a host to change values in
40133 to 40138 the B6000 unit by writing a register
value.
8 Loopback Test Test 0 This is a diagnostic command which
echoes the command sent.
11.4.2 Modbus Error Codes
The T-3 card supports the following Modbus Error Codes:
Code Name Description
0 All OK The module is operating as desired
1 Illegal Functions An illegal function code request is being attempted
2 Bad Data Address The address, or the range of addresses, covered by
a request from the master are not within allowed
limits.
3 Bad Data Value The value in the data field of the command is not
allowed.
4 Incomplete Response This error indicates that an incomplete response was
Detected received to a master query. Often this will indicate
that the slave device may be responding too quickly
or that there may be excessive noise on the line.
6 Module Busy The module busy status code is returned when a
write command from the master has not yet been
completed when a second write command is received