CTI 2572-A Installation and Operation Guide
10
AutoStart using EEPROM Data
If you choose this method, the module will start up using network parameters previously written to
EEPROM. The primary advantage of this approach is that it eliminates the need for additional PLC
logic to initiate startup. See Section
2.10. Storing Network Parameters in EEPROM
.
The downside of this method is that, when installing or replacing modules, you must manually
configure them. In addition, if you arbitrarily swap 2572-A modules between PLCs, the IP address
will move with the module. The effect of inadvertently swapping IP addresses can cause major
problems, since communications directed at one PLC would actually be going to another PLC.
PLC Start
Using this method, PLC logic is used to start the module. A special
Start Network Server
command,
triggered by PLC logic, transfers the network data stored in V memory to the module. An important
advantage to this method is that it eliminates the need to manually configure the module during the
initial installation or during a replacement operation. In addition, since the network parameters are
stored in PLC memory, the module IP address remains associated with the PLC even when modules
are swapped. The primary disadvantage is that it requires a small amount of additional ladder logic. In
addition, if the PLC is not in run mode (not executing logic) the module will not start up. The PLC
logic to perform this function is described in CHAPTER 4. CAMP SERVER COMMANDS.
AutoStart Using DHCP
Using this method, the module obtains its IP address and other network parameters from a Dynamic
Host Configuration Protocol (DHCP). Using a patent pending method, the DHCP server provides
network parameters and other startup information based on the setting of the Module ID switches.
This approach is similar to the technique used by other industrial networks and offers the advantages
of both of the previous methods. No manual configuration is required and no PLC logic is required.
The primary disadvantage is the need to provide and configure a DHCP server. See APPENDIX E.
USING DHCP.
Choosing between TCP and UDP Protocols
Many HMI drivers and OPC servers will allow you to select either TCP (Transmission Control
Protocol) or UDP (User Datagram Protocol) for delivering messages. In addition, some of the 2572-A
client functions allow you to choose between the two. The following information should help you
determine which is right for your situation.
UDP Protocol
The UDP protocol allows you to send a message to another node without previously establishing a
logical connection to the other node. This method, called
connectionless delivery
, uses smaller
network bandwidth, consumes less module resources, and usually results in faster response times.
Although the delivery of UDP messages is not acknowledged by TCP/IP, higher level protocols, such
as CAMP, confirm that the message was received and that the requested service performed.
NOTE:
In most installations, UDP is the preferred protocol for HMI applications that continuously read data
from the PLC.
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