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Up to 125 input registers can be read by a single query using
function code 0x04.
Read, Set Coil Status (0x01, 0x05, 0x0F)
Coil status contains bit-mapped status accessible to the users. In
principle, a coil status can be read, set or cleared by the host
client. Multiple coil status can be read by specifying the index
of bits of the first coil and the number of consecutive coils in a
single query.
Coil status can be read by function code 0x01.
Function code 0x05 set or clear a single coil, and function code
0x0F set or clear multiple coils.
Read Input Status (0x02)
The input status block contains read-only status accessible to the
users. It can be read by using function code 0x02 in the same as
reading coil status.
Error Handling
According to the Modbus specification, the OpenComms NIC
composes the following exception responses to the client if an
exception or error occurs.
NIC Setup and Testing
33
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