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Opto 22 SNAP Ethernet I/O: Frequently Asked Questions (FAQ) pg. 10/12 3.00 Working with the Opto 22 SNAP Ethernet Brain (cont.) When selecting an IP address, use the subnet mask to make sure that the PC and the SNAP Ethernet brain have the same network number and different node numbers. The subnet mask indicates what part of the IP address is the network number (that’s the part that’s “masked” off), and what part is the node number. The node number must be different from the node number of any other device on the same network. Note that a node number of all binary zeroes or all binary ones is invalid. To determine the network number, bitwise AND the IP address with the subnet mask. To determine the node number, bitwise AND the IP address with the bitwise COMPLEMENT of the subnet mask. As an example, take the dedicated network address of 10.0.0.1 with a subnet mask of 255.0.0.0. The resulting network number would be 10, and the node number would be 1. Example: IP address: 10.0.0.1 Subnet mask: 255.0.0.0 Resulting Network Number: 10 Resulting Node Number: 0.0.1 A good starting point for a dedicated network address scheme is 10.x.x.x with a subnet mask of 255.0.0.0. This provides the widest range of node numbers in a single network number. 3.30 What if my SNAP Ethernet I/O system has the same IP address as a PC on my network? If a SNAP Ethernet brain has the same IP address as a PC on the network, the PC will automatically take itself off the network. The Ethernet brain will remain on the network. The PC will display the MAC address (for example: 00-a0-3d-xx-xx-xx) of the conflicting Opto 22 SNAP Ethernet brain. 3.40 What do I do if I can’t ping the SNAP Ethernet brain? The most common reason for not being able to ping the Ethernet brain is incorrect addressing. For example, the brain and the PC may be on different subnets. To fix this, try the following: either change the subnet mask on the Ethernet brain to be on the same subnet as your host, or “widen” the subnet mask so that both IP addresses are on the same subnet. Use IPCONFIG on Windows NT or WinIpCfg on Windows 9x to determine the PC’s IP address. If the brain’s ERD (Ethernet Receive Data) LED blinks while pinging, then the PC is able to transmit and the brain sees that transmission. (Note that this light will also blink if any traffic exists on the network. Look for a pattern of blinking as the ping command executes.) If the brain does not respond, then either the brain is at a different address, or the brain thinks the PC is not on the same subnet. If the steps above don’t work, verify that TCP/IP is installed on your machine. Type PING at the command prompt (DOS window) followed by the loopback address 127.0.0.1. This will ping your own machine (without actually going out on the network) to confirm that the TCP/IP protocol suite is installed. This procedure will not verify correct addressing on your network. For additional troubleshooting help, see the Troubleshooting appendix in Opto 22 Form #1112, the SNAP Ethernet Brain User’s Guide. Opto 22 43044 Business Park Drive Temecula, CA 92590 Phone: (909)695-3000 (800)321-OPTO Fax: (909)695-3095 Internet : www.opto22.com Inside Sales: (800) 452-OPTO Product Support: (800) TEK-OPTO (909) 695-3080 Fax: (909) 695-3017 E-mail: support@opto22.com FaxBack: (800) 474-OPTO
Opto 22 SNAP Ethernet I/O: Frequently Asked Questions (FAQ) pg. 11/12 3.00 Working with the Opto 22 SNAP Ethernet Brain (cont.) _____________________________________________________________________________ 4.00 Setting Up Your Ethernet Hardware 4.10 Where can I find Ethernet hardware? Ethernet hardware products are widely available from many sources. Office supply stores, computer stores, resellers, and the Internet are a few places to look. You can also try any local Internet service provider that has consulting services. For industrial-grade Ethernet hardware connectivity solutions, check out Black Box online at http://www.blackbox.com or Hirschmann at http://www.hirschmann.com. 4.20 What are Ethernet’s cabling requirements? Ethernet packets can exist on several types of media. The Opto 22 Ethernet products support only twisted-pair cabling, commonly referred to as 10BASE-T or 100BASE-X. (The SNAP Ethernet brain also supports packet transmission through the serial port via Point-to-Point Protocol (PPP), but that method is not truly “Ethernet.”) This designation is an IEEE shorthand identifier. The “10” in the media type designation refers to the transmission speed of 10 Mbps. The “BASE” refers to baseband signaling, which means that only Ethernet signals are carried on the medium in a single frequency range. The “T” represents twisted-pair. The actual Ethernet cable is four twisted-pair wires (eight total), commonly referred to as Category 5 cable. Cat 5 cable is the only copper medium tested and certified for use in 100 Mbps environments. On both ends of the cable are connectors, referred to as RJ-45 connectors. The physical length of any 10BASE-T or 100BASE-X Ethernet segment cannot exceed 100 meters. An Ethernet segment is defined as the link between two Ethernet nodes (for example, a computer with a network interface card and a SNAP Ethernet brain) and a port on a hub. However, distances between two Ethernet nodes over several segments can exceed 100 meters by use of repeaters, switches, or mixed media segments such as fiber optic cable. 4.30 How do I connect to Ethernet devices that are more than 100 meters apart? The use of repeater hubs, bridges, routers, or switches will extend the distance between nodes. A node is defined as a connection point on the network. The 100-meter limitation is between two nodes on a 10BASE-T or 100BASE-TX network. (If you use fiberoptics, referred to as 10BASE-FL or 10BASE-FX, the distance between nodes is 2,000 meters. Use of fiber-optic cable is not directly supported by the SNAP Ethernet brain; a fiber-to-copper transceiver is necessary.) For example, the distance between a SNAP Ethernet brain and a repeater hub cannot exceed 100 meters. But then the distance from the repeater hub to your computer could be an additional 100 meters. However, you cannot indefinitely continue to daisy chain hubs to extend the distance of your network. Ethernet must follow the “5-4-3” rule of repeater use: the network can only have five segments connected; it can only use four repeaters; and of the five segments, only three can have users attached to them; the other two must be inter-repeater links. To extend beyond the “5-4-3” rule, the use of bridges, routers, or switches is necessary. Opto 22 43044 Business Park Drive Temecula, CA 92590 Phone: (909)695-3000 (800)321-OPTO Fax: (909)695-3095 Internet : www.opto22.com Inside Sales: (800) 452-OPTO Product Support: (800) TEK-OPTO (909) 695-3080 Fax: (909) 695-3017 E-mail: support@opto22.com FaxBack: (800) 474-OPTO
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