Setup guide

Chapter 2 System Objects
Object Reference Manual 3-54 www.Automationdirect.com
In this example, Lookout
Direct
is connected to a Modbus-speaking PLC
with an address of 5 using serial port 1 (which was previously configured
for hardwired communications), and polling the device every second.
Modbus Serial indicates that the slave device talks either Modbus ASCII
or Modbus RTU. When you select this option, Lookout
Direct
first tries to
communicate using the RTU format. If unsuccessful, it then tries the
ASCII format (a little slower). If your network is susceptible to repeated
communication problems, and if these problems slow scanning
considerably, you may want to disable Lookout
Direct
from retrying both
formats. This can speed communication retries by Lookout
Direct;
however, it will not fix your communication problems. Call National
Instruments technical support to for information on how to prohibit
Lookout
Direct
from trying to communicate using both formats.
Modbus Plus Network indicates that the slave device is connected to the
Lookout
Direct
computer via a Modbus Plus network card.
Note
NetBIOS-based networking software typically uses software interrupt 5C. This is
also the default software interrupt used by the Modbus Plus Network card driver. Change
the Modbus Plus software interrupt from 5C to 5D, 5E, or 5F. Refer to your Modicon
documentation for instructions on changing the software interrupt setting.
Modbus Ethernet indicates you are communicating with the Modbus
slave device using an Ethernet connection.
If you select Modbus Serial, you must specify Address, Serial Port, Data
Rate, Parity, Data Bits, and Stop Bits. And if you are using a Dial-up