Model 672/675 Technical Reference Manual
8-19
While Modbus is specified for a given COMM port, then that port cannot be used to send data native
672/675 commands to the scale. Also, any attempt to send data out a Modbus Comm port will result in the
"NoTxX Allow" message being displayed briefly.
At this time, the scale can only act as a slave on the Modbus ( network. Operation of the Model 672/675 as a
master may be considered sometime in the future if there is deemed to be significant demand for this
capability.
SPECIFYING MODBUS ADDRESS
P209 "MbAdX": This parameter is used to specify the Modbus address which is recognized by the Model
672/675 on the current serial port, as specified by the 'X'. If P205 is not set for "Modbs" then P209 is not
accessible. Enter a value between 1 and 247, or press [ENTER] alone to increment the address by one until
the desired address is displayed.
M
ODBUS
“I
NPUT
” S
ETPOINTS
When a Modbus command is used to turn on or off an input setpoint above #128, the setpoint's current state
is not tested or affected. Therefore, if the setpoint invoked a macro when it turned on, it would still invoke
the macro even if the setpoint should have already been on.
The input type setpoints will not work correctly for setpoints 129-144 due to the way PDIO input setpoints
are handled. Recommend only using setpoint inputs above 144 if invoking macros via Modbus.
In other words, a macro may be invoked via a Modbus command via the following method: Choose a
setpoint above 144 and set it up as an input type that invokes the desired macro upon activation and/or
deactivation. When a Modbus command is received to activate or deactivate that setpoint, the macro will be
invoked.
M
ODBUS
P
ROTOCOL
(RTU M
ODE
)
RTU (Remote Terminal Unit) messaging framing is used on a Modbus network in place of ASCII message
framing. With this method of framing, each 8-bit byte is the equivalent of 2 ASCII characters. The main
advantage of this mode over ASCII is that there is greater character density allowing better data throughput
for the same baud rate.
Note: The following information pertains to setting up the 672/675 for Modbus networks with RTU framing.
The following examples are 672/675 setups for slave operation on a Modbus network with RTU framing. To
make use of this protocol with the 672/675 requires existing knowledge of the Modbus protocol. For any
further information on Modbus Protocol and ASCII & RTU framing, refer to the following document.
Modicon™, Modbus Protocol Reference Guide, PI-MBUS Rev. G
Notes on Using MODBUS RTU on 672/675:
• Works only on comm port 1
• 8 data bits are forced regardless of P201.1
• Flow control is forced to none regardless of P204.1 (also forced now for ASCII mode)
Setup mode:
• Set Modbus receive type
• Set Modbus address
• Set Modbus mode to RTU instead of ASCII at P210
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