75
The physical interface for Modbus-RTU is
isolated RS-485. Therefore, the limitations and
restrictions according to the RS-485 standard
must be observed. In particular, the total length
should not be more than 1,000m per network and
each network should be daisy- chained with not
more than total 32 devices.
In the Modbus TCPIP (only for DPM680)
interface, the physical interface is 10M/100M
Base T Ethernet, based on IPv4. The meter
may auto-negotiate with the PC or router
whenever possible to run at 100M Base T speed
if available.
5
MoDBus opEraTions
The meter is accessible through either Modbus-
RTU or Modbus TCPIP (only for DPM680).
The table of variables and their respective
addresses are similar for both protocols
and they are listed in the DPM680 Modbus
Communication Manual which can be
downloaded from the www.itmikro.com website.
The Modbus registers are divided into 4 broad
categories:
• Device Information Data
• Communication Information Data
• Setting Data
• Operations Data
The registers in ALL categories can be accessed
through either function code 03 or 04. Only
Setting Data registers can be overwritten through
function code 06. Function code 06 can only
be enabled through the meter touch buttons –
please see section 3.8.2.2.
noTE:
It is NOT advisable to access the meter through
both RTU and TCP/IP at the same time.
noTE:
The device ID is xed at 1 for Modbus TCP/IP.
The Modbus server is limited to opening no
more than 2 TCP/IP sockets, i.e. it cannot
serve more than 2 clients.
Modbus Operations 5
To Next Page
Loading...
