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TASK 6 (Modbus TCP Option)
M
ODBUS
TCP C
ONFIGURATION
6.1 Enable Modbus TCP Protocol
The AMCI Net Configurator utility can be used to change the communications protocol used by the
SMD23E2 or SMD24E2. This is typically done while setting the IP address. Specifically, follow the
steps in section 2.2c,
Use the AMCI NET Configurator Utility
6.2 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.
6.2.1 Modbus Table Mapping
The Discrete Input and Input Register tables in the Modbus data model map to the same physical memory
locations in the SMD23E2 or SMD24E2 units.
These registers hold data that is reported from the driver to the host controller. This data is typically
command responses and status data.
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 SMD23E2 or SMD24E2 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.
6.2.2 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 SMD23E2 or SMD24E2 to your host controller. Refer to
your host controller’s documentation for information on how to accomplish this.
An AMCI SMD23E2 or SMD24E2 that has been configured for the Modbus TCP
protocol requires a host controller to issue configuration data and motion com-
mands to the unit. This chapter tell you how the I/O words used by an AMCI
SMD23E2 or SMD24E2 are mapped to the Modbus I/O registers.
† MODBUS Application Protocol Specification V1.1b3, section 4.3: MODBUS Data model.
www.modbus.org
