AMCI NEXUS NX2A4E2, User Manual

Page: 68 / 76

M
ODBUS
TCP C
ONFIGURATION
Modbus TCP Protocol
ADVANCED MICRO CONTROLS INC.
68
AMCI Modbus TCP Memory Layout
The NX2A4E2 has a starting Input Register address of 0 and a starting Output Register address of 1024. Input
Registers hold the data from the NX2A4E2 while Output Registers hold the data to be written to the unit. Fig-
ure T5.6 shows how an NX2A4E2 is mapped to the Modbus data reference. The complete specification for
the Modbus protocol can be downloaded at http://www.modbus.org/specs.php.
Figure T5.6 Modbus Data Reference Map
You must read all twenty-one input registers and write all ten output registers, even if those
register contain no meaningful data. The NX2A4E2 uses dual port memory and does not
switch banks until the last register is read from or written to. If you do not read from or write
to all of the registers, the NX2A4E2 will never switch banks and the network data will never
update.
Supported Number of Connections
All NX2A4E2 units support five concurrent connections. When connections exist, the Network Status (NS)
LED on the unit will flash green. The number of blinks indicate the number of active connections. There is a
two second break between groups of flashes.
Network Input
Data
Not Implemented
Network Output
Data
LSB and MSB
Numbers
Mapped as:
Discrete Inputs
Holding Registers
Input Registers
Mapped as:
Coils
Holding Registers
Register 1024
Register 1033
16,384 16,399
16,528 16,543
Register 20
320 335
0 15
Register 0