TECHNICAL NOTE 7-1. ARCNET Cable Length vs. Number of Nodes for the HYC9088 in Coaxial Bus Topology By: Daniel Kilcourse May 1991.

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1 TECHNICAL NOTE 7-1 ARCNET Cable Length vs. Number of Nodes for the HYC9088 in Coaxial Bus Topology By: Daniel Kilcourse May 1991 Page 1

2 80 Arkay Drive Hauppauge, NY (631) FAX (631) Copyright SMSC All rights reserved. Circuit diagrams and other information relating to SMSC products are included as a means of illustrating typical applications. Consequently, complete information sufficient for construction purposes is not necessarily given. Although the information has been checked and is believed to be accurate, no responsibility is assumed for inaccuracies. SMSC reserves the right to make changes to specifications and product descriptions at any time without notice. Contact your local SMSC sales office to obtain the latest specifications before placing your product order. The provision of this information does not convey to the purchaser of the described semiconductor devices any licenses under any patent rights or other intellectual property rights of SMSC or others. All sales are expressly conditional on your agreement to the terms and conditions of the most recently dated version of SMSC's standard Terms of Sale Agreement dated before the date of your order (the "Terms of Sale Agreement"). The product may contain design defects or errors known as anomalies which may cause the product's functions to deviate from published specifications. Anomaly sheets are available upon request. SMSC products are not designed, intended, authorized or warranted for use in any life support or other application where product failure could cause or contribute to personal injury or severe property damage. Any and all such uses without prior written approval of an Officer of SMSC and further testing and/or modification will be fully at the risk of the customer. Copies of this document or other SMSC literature, as well as the Terms of Sale Agreement, may be obtained by visiting SMSC s website at SMSC is a registered trademark of Standard Microsystems Corporation ( SMSC ). Product names and company names are the trademarks of their respective holders. SMSC DISCLAIMS AND EXCLUDES ANY AND ALL WARRANTIES, INCLUDING WITHOUT LIMITATION ANY AND ALL IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, TITLE, AND AGAINST INFRINGEMENT AND THE LIKE, AND ANY AND ALL WARRANTIES ARISING FROM ANY COURSE OF DEALING OR USAGE OF TRADE. IN NO EVENT SHALL SMSC BE LIABLE FOR ANY DIRECT, INCIDENTAL, INDIRECT, SPECIAL, PUNITIVE, OR CONSEQUENTIAL DAMAGES; OR FOR LOST DATA, PROFITS, SAVINGS OR REVENUES OF ANY KIND; REGARDLESS OF THE FORM OF ACTION, WHETHER BASED ON CONTRACT; TORT; NEGLIGENCE OF SMSC OR OTHERS; STRICT LIABILITY; BREACH OF WARRANTY; OR OTHERWISE; WHETHER OR NOT ANY REMEDY OF BUYER IS HELD TO HAVE FAILED OF ITS ESSENTIAL PURPOSE, AND WHETHER OR NOT SMSC HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. Page 2

3 Introduction The original ARCNET star topology networks, those which make use of the LAND (Local Area Network Driver - HYC9068) module, are straightforward with respect to cable lengths and the number of nodes. Simply stated, the user is allowed a maximum distance of 2000 feet between any two devices containing a LAND module. Permissible distances become somewhat of a more complicated issue when dealing with the bus topology, made possible by the HIT (High Impedance Transceiver - HYC9088) module and worse when combining the two types of modules on a single cable. This technical note addresses the coaxial cable length vs. number of nodes issue for HIT only topologies, as well as HIT/LAND topologies. Twisted Pair issues do not fall within the scope of this technical note. Device/Module Identification Table 1 lists SMSC ARCNET products and indicates the type of module used in each product. DEVICE PC110 PS110 Active Hub-01 Active Hub-Opt PC210 Active Link Active Link-Opt Active Link-Opt 2 Twisted Pair Link Table 1 MODULE LAND LAND LAND (all ports) LAND (coax ports only) HIT HIT (both ports) HIT Only Topologies SMSC has specified that eight nodes may be connected to 1000 feet of RG62 coaxial cable. In fact, more nodes may be connected if the cable is shorter and fewer nodes are allowed if the cable is longer. A node, for the purposes of this discussion, is defined as any device containing a HIT and is connected to the cable. A HIT will output a signal 9 db over and above that required to drive its own receiver and insure proper signal to noise ratio for the remaining nodes. Each additional node has an insertion loss of 0.43 db and RG 62 cable has an attenuation of 0.6 db per 100 feet at 5 MHz (5 MHz is the frequency generated when transmitting a logical "one"). Based on this information, a chart may be made to show the maximum cable length for a given number of nodes. Refer to Table 2. Due to transmission line effects, SMSC does not recommend using more than 19 nodes on a single cable. Additionally, SMSC does not recommend the use of passive hubs with any HIT-type product. Page 3

4 Table 2 - Cable Length vs. Number of Nodes NUMBER OF NODES INSERTION LOSS REMAINING POWER MAXIMUM CABLE LENGTH db 8.57 db 1428 feet db 8.14 db 1356 feet db 7.71 db 1285 feet db 7.28 db 1213 feet db 6.85 db 1141 feet db 6.42 db 1070 feet db 5.99 db 998 feet db 5.56 db 926 feet db 5.13 db 855 feet db 4.70 db 783 feet db 4.27 db 711 feet db 3.84 db 640 feet db 3.41 db 568 feet db 2.98 db 496 feet db 2.55 db 425 feet db 2.12 db 353 feet db 1.69 db 281 feet db 1.26 db 210 feet HIT/LAND Bus Topology Although not recommended, the HIT and LAND modules may be mixed on a single cable. If you choose to mix the two modules, the following rules must be observed: 1. The cable must be RG62 type cable. 2. LAND modules may be connected ONLY at the ends of the cable. 3. Since the LAND provides the proper termination impedance, the terminator typically connected to the end of the cable in the bus topology must NOT be connected. 4. Use Table 2 to determine the maximum cable lengths for the number of desired nodes. In a mixed HIT/LAND environment, do NOT count devices containing LAND modules as nodes. 5. A device containing a LAND module must ALWAYS have power applied. If power is lost, the cable will no longer be terminated properly and may result in a non-functioning network. Once, again, the HIT/LAND Bus topology is NOT recommended but is presented above for those who find it necessary to use this topology in their application. Questions and Answers 1. Can a HIT-type device be connected to an existing star configuration which has 2000 feet of cable and a LAND-type device at each end? A HIT device presents an additional.43 db loss to the network. This is equivalent to approximately 72 feet of RG62 cable. A HIT device may be connected to a cable 1928 feet long (2000 ft ft.) which has a LAND device on each end providing the distance between the HIT device and the furthest node is no greater than 1500 feet. Page 4

5 2. With respect to termination characteristics, how does the HYC9068 (LAND) differ from an HYC9088 (HIT) which is terminated externally with a 93Ω resistor? The HYC9068 (LAND) has a 93Ω impedance only when power is applied to the device. An HYC9068 must have power applied for it to function properly as a terminator. The HYC9088 (HIT) maintains a high impedance whether power is applied or not. This allows a HIT to be placed anywhere on the cable. When a HIT and a 93Ω resistor are connected to the end of a cable, it is the resistor which provides the actual termination. To summarize, with power applied, there is no difference between a LAND and a HIT with a 93Ω resistor. With power removed, a LAND will lose its terminating property while the HIT with a 93Ω resistor will maintain its terminating property. 3. Can a HIT be connected to a Passive Hub? No. Due to their heavy load and short cable length restrictions, the use of Passive Hubs with HITS is not allowed. 4. Can a HIT be used to directly drive Twisted Pair cable? Yes. The HYC9088 may directly drive either coaxial or twisted pair cable in a Bus topology. 5. Is RG62 cable required when connecting only HIT-type ARCNET products on a common cable? Other types of coax cable may be used to connect HIT-type ARCNET products providing the cable is terminated with a resistor of a value equal to the characteristic impedance of the cable. Keep in mind that the attenuation of other types of cable may be different from that of RG62 and, therefore, affect the maximum cable length for a given number of nodes. The frequency of concern is 5 MHz. RG62 will work with both HIT- and LAND-type devices while other type cabling is acceptable for the HIT but not the LAND. If your network topology is expected to change, and they do change from time to time, you should not consider cable other than RG If given the choice of purchasing a LAND-type product or a HIT-type product, which should I buy? HIT-type products offer more flexibility. They can be connected to any point on the cable, providing they are at least six feet apart, with power applied or removed. LAND-type products may only be connected to the ends of the cable. The cable must be RG62 and power must always be applied. When in doubt, purchase the HIT-type product. Conclusion ARCNET maintains a rapid growth rate in the network environment. The HIT module, allowing a more flexible network architecture, is a primary reason for this rapid growth. Offering products which address Twisted Pair, the migration towards CMOS and higher levels of integration also contribute strongly to the wide acceptance of ARCNET. Standard Microsystems Corporation is committed to the ARCNET product line and will continue to offer reliable, state-of-the-art products. Page 5