OPTO 22 SNAP-PAC-EB1, Руководство пользователя

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NETWORKING
SNAP PAC Brains User’s Guide
14
Connecting the Brain Directly to a PC or Controller
A direct connection using a standard Ethernet cable connects the SNAP PAC brain with one host,
either a PC or a controller. (A crossover cable is not required for direct connection to a host.) You can
use either Ethernet interface on the brain for the connection. Additional SNAP PAC brains can be
daisy-chained from the first brain using the brain’s second Ethernet network interface, which acts as
a network switch. See
“Using SNAP PAC Brain Network Interfaces” on page 15 for more information.
If you need only a small control or monitoring network and have no existing Ethernet network, a
direct connection is ideal. It’s quick, easy, and inexpensive because it requires only cables (no
separate Ethernet switches or routers). It also provides high speed and high security for a small
system.
A direct connection is also useful for assigning an IP address, configuring I/O points, and testing
applications. The direct connection eliminates other variables that could interfere with
communication, so you can focus on maintenance and troubleshooting.
Attaching the Brain to an Existing Ethernet Network
The first rule in attaching SNAP PAC brains to an existing network is to work closely with your system
administrator, who must determine network topology and hardware. Be sure to consider the impact
on your existing network of adding the brains. For best performance, use a 100 Mbps network.
In addition, make sure the system administrator understands that each brain must have a fixed
(static) IP address, whether or not a Dynamic Host Configuration Protocol (DHCP) server is used on
the network. For more information on IP addresses, see the PAC Manager User’s Guide .
Because the SNAP PAC brain has two switched Ethernet interfaces, the brains can optionally be
daisy-chained together. (See
“Using SNAP PAC Brain Network Interfaces” on page 15 .)
If you need to isolate the control system data from the main network backbone, you can use a router,
network switch, or other gateway device. You can also use a SNAP PAC controller, which has two
independent Ethernet network interfaces: one interface can be connected to the enterprise network,
and the other used for the control system. See Opto 22 form #1696, the
SNAP PAC System Data Book ,
for more information on network options.
Using the Brain in an Independent Network
The third way SNAP PAC brains can be used is by developing an independent network. An
independent network gives a high level of communication speed and volume, as well as high
security. You may also need a separate network for critical control applications. Again, the choice
depends on your requirements for data transactions, data security, and whether a near-deterministic
system is necessary.
If you are building your own network, remember that each brain must have a fixed IP address. See
the PAC Manager User’s Guide for more information on IP addresses.
If you have no existing Ethernet network, you can use off-the-shelf Ethernet components to build
one. Since Ethernet and TCP/IP are worldwide standards, there are a number of commercially