AMCI NEXUS NX2A4E2, Руководство пользователя

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Modbus TCP Reference
M
ODBUS
TCP C
ONFIGURATION
Enable Modbus TCP Protocol
The internal web page utility can be used to change the communications protocol used by the NX2A4E2. This
is typically done while setting the IP address. Specifically, follow the steps in section 2.2c,
Use the Embed-
ded Web Server which starts on page 45.
Modbus Addressing
The register addresses used in this manual are the Modbus logical reference numbers
†
, which are unsigned
integers starting at zero. This is often called zero based addressing. In this scheme, the first register is given
an address of zero. This is the actual addressing scheme used in the Modbus packets.
Another common addressing scheme is one based or data model addressing. In this scheme, the register’s
number is used as its address, so the first register, Register 1 in the data model, has an address of 1.
Modbus Table Mapping
The Discrete Input and Input Register tables in the Modbus data model map to the same physical memory
locations in the NX2A4E2 units.

These registers hold data that is reported from the NX2A4E2 to the host controller.

Addresses for these registers and inputs start at 0 in zero based addressing.
As examples:

Discrete Input 0 is the same memory location as bit 0 of the first Input Register.

Register address 3, the fourth register, contains Discrete Inputs 48 through 63.
The Coil and Holding Register tables in the Modbus data model map to the same physical memory locations
in the NX2A4E2 units.

These registers hold data that is from the host controller to the unit. This data is typically commands.

Addresses for these registers start at 1024 in zero based addressing. Coil addresses start at 16,384 in
zero based addressing (1024*16).
As examples:

Coil 16384 is the same memory location as bit 0 of the first Holding Register.

Register address 1025, the address of the second Holding Register, contains Discrete Inputs 16,400
through 16,415 in zero based addressing.
Host Addressing
Your host controller may not use these basic addressing schemes for communicating over a Modbus connec-
tion. For example, Modicon controllers use addresses starting at 30000 for Input Registers and addresses
starting at 40000 for Holding Registers. GE hosts internally use their %R memory for Holding Registers and
%AI memory for Input Registers.
If this is the case, you will define a mapping between your host controller’s addressing scheme and the zero
based Modbus TCP addresses when you add the NX2A4E2 to your host controller. Refer to your host control-
ler’s documentation for information on how to accomplish this.
An AMCI NX2A4E2 that has been configured for the Modbus TCP protocol
requires a host controller to issue configuration data and read data from the unit.
This chapter tell you how the I/O words used by an AMCI NX2A4E2 are mapped to
the Modbus I/O registers.
† MODBUS Application Protocol Specification V1.1b3, section 4.3: MODBUS Data model.
www.modbus.org