Emerson MONITORING OpenComms Manuel D’Utilisation

The OpenComms NIC implements the following Modbus functions. 

However, integrators will use function code 0x03, and 0x06 most often 

due to the type of data to be acquired.

A holding register is a 16-bit message unit. In principle, a message in 

a holding register is write / readable, but holding registers can be used 

by read-only data as well. Holding registers are mapped into 

40001-49999 logic address range.
Holding registers can be read by function code 0x03. A maximum of 

125 registers can be read by a single query.
Function code 0x06 requests the server to change the content of a sin-

gle holding register, and function code 0x10 requests server to change 

the contents of multiple holding registers adjacent to each other.

The input register block contains read-only data accessible to the user. 

A datum in the input register block occupies one or multiple registers 

such as described in the previous section. The input registers are 

mapped into 30000-39999 of the logic address range.
Up to 125 input registers can be read by a single query using function 

code 0x04.

Coil status contains bit-mapped status accessible to the users. In prin-

ciple, a coil status can be read, set or cleared by the host client. Multi-

ple 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.

0x01

Read Coil Status

0x02

Read Input Status

0x03

Read Holding Registers

0x04

Read Input Registers

0x06

Write Single Holding Register

0x0F

Force Multiple Coils

0x10

Preset Multiple Holding Registers