ARCNET
NOTE: This page is an
attempt to go from "Zero to Hero" in a short time. I have
NEVER even touched
ARCNET, so don't run off thinking you are gonna re-wire all
the controllers on a plant floor after reading this.If you are in an industrial or business setting, I HIGHLY recommend that you contact folks that saavy ARCNET, after all, how much is your time worth?
SMC HYC9068 Datasheet
NCR 90C26 Datasheet
SMC ARC NET Local Area Network Controller Designer's Guide
SMC ARCNET Drivers Ver 3.2
Thomas-Conrad ARCNET Drivers Ver 2.10
Thomas-Conrad TCNS Drivers Ver 1.20
ARCNET Tutorial
ARCNET Trade Association from Internet Archive
Contemporary Controls Mothership of ARCNET info
Arcnet MCA Project Salvador Garcia
Of all of the niche network architectures to still be alive and kicking is ARCNET. It can operate long distances and is deterministic, things that are real good for industrial applications.
Hubs [OMG]
Hubs facilitate cabling by interconnecting multiple NIMs and, in most cases, they exercise no control over the network. The primary function of a hub is to provide a convenient method of expanding a network. There are two types of hubs that can perform this task—a passive hub or an active hub
Passive Hubs—Passive hubs are inexpensive, require no power and their sole purpose is to match line impedances, which they do with resistors. These hubs usually have four ports to connect four coaxial star transceivers. One of the disadvantages of these hubs is that they limit the network to 200 feet and each segment of the network to 100 feet. Also, unused ports must be terminated with a 93 ohm resistor for proper operation. Passive hubs are used on small (four nodes or less) coaxial star networks.
Active Hubs—Active hubs are essentially electronic repeaters. Although they require power, active hubs support all cabling options, support longer distances than passive hubs, provide isolation and guard against cabling faults and reflections. These are the hubs which are used to cable distributed star networks.
Unused ports on an active hub need not be terminated. Unlike passive hubs, active hubs do not attenuate signals and can be cascaded. A cable failure will affect only one port on an active hub. Active hubs are available as either internal or external devices. Internal hubs reside inside a computer that also has a NIM, while
external hubs are stand-alone devices.
Active hubs can be configured as two port devices as well. A link is a two port device with differing cable options on each port allowing for the transition of one medium type to another such as coaxial to fiber conversion. A repeater is a two-port device of the same cable option.
ARCNET Topologies
Point-To-Point In the point-to-point connection, only two NIMs are used. This is the simplest of networks. Each NIM effectively terminates the other NIM; therefore, no hub is required.
Star - The star connection requires hubs. Each NIM connects to one point on the hub that effectively terminates the connected NIM. Since only one NIM is connected to any one hub port, faults in a cable or at a node can be easily isolated. Cabling a facility is often easier with a star topology
Distributed Star [Tree] —If several active hubs are used, a distributed star topology can be implemented. This topology is the most flexible cabling method available in ARCNET LANs since both node-to-hub and hub-to-hub connections are supported. Two or more active hubs, each supporting a cluster of connected nodes, are linked together by a “home run” cable.
The distributed star topology helps reduce cabling costs since each node connects to a local hub, thereby eliminating the need to run each node’s cable over to one wiring location. Like the star configuration, nodes are isolated from one another.
NOTE: The "Home Run" cable from Active Hub to Active Hub is not terminated.
Bus In the bus configuration, NIMs equipped with high impedance transceivers or EIA-485 drivers must be used. Using RG-62/u coaxial cable and BNC “tees,” or twisted-pair cable, several NIMs can be connected without the use of a hub. Termination is provided by the installation of a resistive terminator at both ends of the cable segment. The advantage of this configuration is that no hub is required. The disadvantage is that one node failure could disrupt the complete network. Also, cabling distances are less than the star or point-to-point connection.
NOTE: There is a terminator at the leftmost NIM and one after the rightmost NIM.
Multidrop [Not Allowed!] A multidrop topology is a variation of the bus topology where a short “drop” cable from the tee connection is allowed. There has not been any study on the effects and limitation of drop cables so this topology is not allowed.
Star/Bus To bridge a bus topology to a star requires an active hub. In this case, the active hub acts as both a terminator for the bus and a repeater for the network. Remove the passive terminator from one end of the bus and connect that end to one port on the active hub. Other ports on the active hub can now be used for other bus or star connections.
NOTE: The "Bus" segment to the left of the Active Hub has the furthest node Terminated, the cable into the Hub is not terminated. Set the NIMs on the "Bus" segment to "Bus" mode. Set the NIMs that are directly connected to the Hub to "Star" mode.
Daisy-Chain Daisy chaining of NIMs requires two connectors or a single connector with redundant connections per NIM. Internally the two connections are bussed together and, therefore, do not truly represent a daisy-chain connection but that of a bus. Daisy chaining is best used with RJ-11 connectors. The unused connectors at each end of the daisy-chain can then be used with RJ-11 style terminators.
Ring [Not Allowed!] ARCNET does not allow for a ring or a loop connection. Unreliable operation of the network will be experienced if a loop is implemented or if a distributed star topology is violated by introducing a loop connection back to any one node.
Auto-Reconfiguration [Wall of text]
Another feature of ARCNET is its ability to reconfigure the network automatically if a node is either added or deleted from the network. If a node joins the network, it does not automatically participate in the token-passing sequence. Once a node notices that it is never granted the token, it will jam the network with a reconfiguration burst that destroys the token-passing sequence. Once the token is lost, all nodes will cease transmitting and begin a timeout sequence based upon their own node address. The node with the highest address will timeout first and begin a token pass sequence to the node with the next highest address. If that node does not respond, it is assumed not to exist. The destination node address is incremented and the token resent. This sequence is repeated until a node responds. At that time, the token is released to the responding node and the address of the responding node is noted as the logical neighbor of the originating node. The sequence is repeated by all nodes until each node learns its logical
neighbor. At that time the token passes from neighbor to neighbor without wasting time on absent addresses.
If a node leaves the network the reconfiguration sequence is slightly different. When a node releases the token to its logical neighbor, it continues to monitor network activity to ensure that the logical neighbor responded with either a token pass or a start of a transmission sequence. If no activity was sensed, the node that passed the token infers that its logical neighbor has left the network and immediately begins a search for a new logical neighbor by incrementing the node address of its logical neighbor and initiating a token pass. Network activity is again monitored and the incrementing process and resending of the token continues until a new logical neighbor is found. Once found, the network returns to the normal logical ring routine of passing tokens to
"If you cut an ARCNET, you get two ARCNETs within seconds..."
This will require meditation, as termination and hubs are an important part of the "Auto-Reconfiguration" aspect.
Transceivers [Robots in disguise?]
Coaxial Star—Typically, ARCNET is cabled with RG-62/u coaxial cable (with BNC connectors) in a star topology, each NIM connects directly to a port on an active or passive hub. Alternatively, RG-59/u coaxial cable can be used, but at a cost of
reduced distances between a node and a hub. Overall, coaxial cable offers good performance, good noise immunity, low propagation delay, low signal attenuation, sufficient ruggedness and low cost. The coaxial star configuration also provides the
longest coaxial distance and simplified troubleshooting.
Coaxial Bus—RG-62/u coaxial cable can be used in a bus configuration using BNC tee connectors with passive terminators at each end of the cable. Although hubs are not required, cabling options are restricted and troubleshooting is much more difficult. There is a minimum distance between adjacent nodes. Coaxial bus is used when reliable coaxial cable communication is required in a hubless system when shorter distances are involved.
Twisted-Pair Star—Unshielded twisted-pair wiring such as IBM Type 3 (#24 or #22 AWG solid copper twisted-pair cable or telephone wiring) can be used. BALUNs are required at both the hub and NIM to use this cable. Some twisted-pair NIMs and hubs have internal BALUNs, so external BALUNs are not needed. Twisted-pair is convenient to install. However, its attenuation exceeds coaxial, its noise immunity is less, and its maximum length between a node and a hub is lower. RJ-11 connectors are often used with this cable.
Twisted-Pair Bus—The convenience of twisted-pair wiring can be used in a bus configuration without the use of BALUNs. Dual RJ-11 jacks are provided so modules can be wired in a “daisy chain” fashion even though electrically they are connected as a bus. Distances are limited as well as node count. Passive terminators are inserted in unused jacks at the far end of the segment. For small hubless systems this approach is attractive.
Glass Fiber Optics and EIA-485 are not covered in this page.
Cable
Coaxial Cable—RG-62u was the original choice for cabling ARCNET systems, and is recommended over RG-59/u if possible. RG-62/u (93 ohm) is a better impedance match to the coaxial transceiver and has less attenuation than RG-59/u (75 ohm) yielding greater distances. Standard BNC connectors and tees are used. Coaxial cable is relatively inexpensive and provides the highest propagation factor compared to other alternatives.
Coaxial Star vs. Bus
The coaxial star transceiver and the coaxial bus transceiver both receive P1 and P2 signals and generate dipulse signals. However, the star transceiver represents a low impedance (approximately 93 ohms) at all times while the bus transceiver represents a high impedance when idle allowing for multiple transceivers to be attached to a common bus. Since the two transceivers have a similar appearance, it is important to distinguish one from another. The following practice is recommended for identification purposes. For star transceivers, use black bodied BNC connectors on the printed-circuit board. For bus transceivers, use white.
The capabilities of the two transceivers differ significantly. The star transceiver can drive 2000 feet (610 m) of RG-62/u cable while the bus can only drive 1000 feet (305 m). However, the bus transceiver can support eight nodes on a single segment. Connections between nodes are made with BNC tee connectors and coaxial cables of at least six feet (2 m) in length. Passive termination is required at the ends of bus segments. The isolation of the two transceivers is typically 1000 volts DC.
Twisted-Pair—Unshielded twisted-pair cabling can be used with several transceivers including those for EIA-485. We recommend IBM type 3 (although other unshielded twisted-pair cable with similar characteristics will also work). Twisted-pair cable is inexpensive and convenient to use and easy to terminate. However, twisted-pair cable has much greater attenuation than coaxial cable and, therefore, has limited distance capability
Twisted-pair is also a popular cabling technology. It is inexpensive and easy to terminate. However, it has much higher attenuation than coaxial cable limiting its use to shorter distances. Frequently, modular jacks and plugs are used to interconnect segments. Twisted-pair cable can be used with conventional coaxial star transceivers if a BALUN is used between the cable and the transceiver. A MUX LAB 10070 is recommended for use as an external BALUN. It has a male BNC connector at one end and a RJ-11 jack at the other, and it must be used only with coaxial star transceivers. For convenience, some vendors provide a product that eliminates the need for external BALUNs. The twisted-pair star transceiver incorporates an internal BALUN along with a coaxial star transceiver together as one unit. Simply connect to the provided RJ-11 jack. When using BALUNs, only star and distributed star topologies are supported. No phase reversal of the wiring is allowed. Many modular plug patch cables invert the wiring. To test for this, hold both ends of the cable side by side with the retaining clips facing the same direction. The color of the wire in the rightmost position of each plug must be the same if there is no inversion of the cable. If this is not the case, the cable is inverted
Twisted-Pair Bus
For hubless systems, twisted-pair bus transceivers can be used. Since modular jacks are used and a bus connection is required, two jacks, internally wired together, are provided on each NIM. Field connections are then made in a daisy-chain fashion to each successive NIM. The remaining end jacks are then plugged with passive terminators. A modular plug terminator is available for this use. Each daisy-chain cable must not invert the signals and must be at least six feet long for reliable operation.
Hubs can be used to extend twisted-pair bus segments. Use a twisted-pair star hub port in place of the passive terminator at one end of the segment. Connect this last port on the NIM to the twisted-pair star port on the hub using an “inverted” modular plug cable. This is necessary since the BALUN in the twisted-pair star port creates a signal inversion that is not compatible with the twisted-pair bus port. The interconnecting inverted cable “rights” the signal. Connect the second twisted-pair bus segment in a similar fashion using an additional twisted-pair star port.
Q171891: Windows 95 Uses Encapsulated Arcnet
A computer running Microsoft Windows NT on an ARCNET network will have difficulty communicating with computers running Windows 95 and Windows 98 on the same network. This is because Windows NT uses Raw ARCNET, while Windows 95 and Windows 98 use Encapsulated ARCNET. The workaround solution is to install the 16-bit TCP/IP stack with Novell Open Data-link Interface (ODI) drivers on the machines running Windows 95 and Windows 98.