Multi-Tech Systems 7500 - Manual (Page 79)

ION 7500 / ION 7600 User’s Guide Using the Modbus/TCP Protocol
Chapter 3 - Default Meter Functionality Page 79
You can use the Modbus RTU protocol to write values into ION external numeric,
pulse and Boolean registers, allowing you to enable, disable and reset meter
functions. You can also use the Modbus protocol to change setup register values in
various ION modules to configure the meter’s operation.To bring data into the
meter with Modbus RTU, you must disable the meter’s password security.
Information about writing ION registers through Modbus is available in the
ION 7500 / ION 7600 Series meter Modicon Modbus Serial Communications Protocol
document.
Using the Modbus/TCP Protocol
Modbus/TCP is the newest open Modbus protocol variant (formerly called
MBAP). It defines the packet structure and connection port (port 502) for the
industry standard TCP/IP protocol. The structure of Modbus/TCP is very similar
to the Modbus RTU packet except that it has an extra six-byte header and does not
use the cyclic redundancy check (CRC). Some of the newest ION firmware now
supports Modbus/TCP for direct communications with the meter.
Modbus/TCP retains the Modbus RTU limit of 256 bytes to a packet. It is suggested
that higher through-put is possible if this limitation is removed. This variant is
called Enhanced Modbus/TCP but, so far, few devices have moved to support it.
Modbus TCP Communications
You can now communicate to the meter via Modbus TCP (formerly called MBAP).
Your meter must have the optional Ethernet port. Connect to socket 502.
Be aware that you cannot form an EtherGate to the Modbus TCP network.
Ethernet
Connect to socket 502