1、INTERNATIONAL STANDARD ISO/IEC 8482 Second edition 1993-l 2-l 5 Information technology - Telecommunications and information exchange between systems - Twisted pair multipoint interconnections Technologies de /information - TcUcommunications et - a binary and bi-directional signal transfer of the int
2、erconnected endpoint systems; - the electrical and mechanical design of the endpoint system branch cables and the common trunk cable, which may be up to 1 200 m in length; - the component measurements of the integrated circuit type generators and receivers within the endpoint systems; - the applicab
3、le data signalling rate up to 12,5 Mbit/s. 1.2 The defined electrical component charac- teristics and measurements are in close conformance with the twisted pair point-to-point characteristics given in ITU-T Recommendation V.11. 1.3 This International Standard does not de- scribe a complete physical
4、 interface and has no functional interface characteristics, such as - number of interchange data and control circuits; - type, size and pin allocation of the endpoint system and branch trunk cable connectors: - data and control signal encoding; - time relations between signals on the interchange cir
5、cuits; - mode of synchronous or asynchronous trans- mission; - signal quality for transmission and reception. 1.4 This International Standard does not specify special environmental conditions, such as galvanic isolation, electromagnetic interference (EMI), radio frequency interference (RFI), and hum
6、an safety. This may form the subject of a future amendment. 1.5 This International Standard is primarily a component specification. It is not sufficiently specified for satisfactory interoperation in all possible configurations. It is the responsibility of implementors to ensure that their intended
7、configuration will allow satisfactory interoperation. 1.6 This International Standard may be com- bined with any appropriate set of functional and additional environmental characteristics so as to meet the practical data transmission requirements in the field of local or wide area networks. 2 Normat
8、ive reference The following ITU-T Recommendation contains certain provisions which, through reference in this text, constitutes provisions of this International Standard. At the time of publication, the edition indicated was valid. All CCITT Recommendations and International Standards are subject to
9、 revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the recommendation indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. The ITU-T Secretari
10、at maintains a list of currently valid ITU-T Recommendations. 1 ITU-T Recommendation V.ll :1988, Electrical characteristics for balanced double-current inter- change circuits for general use with integrated circuit equipment in the field of data communications. 3.6 differential mode voltage: The vec
11、tor difference of the voltages between each conductor of a balanced interchange circuit and ground or other stated voltage reference. NOTE - The differential mode voltage is commonly referred to as the transverse mode voltage. 3 Definitions For the purposes of this International Standard the followi
12、ng definitions apply: 3.1 balanced interchange circuit: An interchange circuit which uses two conductors and the differential mode voltage for transmitting signals. 3.2 common mode ejection ratio (CMRR ): For balanced interchange circuits, the ratio of an applied common mode voltage, V, to the resul
13、ting transverse voltage V, (same as the differential mode voltage). The ratio is normally expressed in decibels as V CM RR = 20 log F tr NOTE - The rejection ratio depends upon the circuit termination and should be measured while terminated in normal use. 3.3 common mode voltage: One half the vector
14、 sum of the voltages between each conductor of a balanced interchange circuit and ground or other stated voltage reference. NOTE This voltage may be a transmitted (or received) signal or noise intereference. In the latter case, this voltage is generally not the same as the voltage, which is sometime
15、s referred to as common mode voltage, that may exist (in a common mode) between the ends of an interchange circuit pair as a result of induction or ground- reference potential difference. 3.4 cross-talk loss (near end): For two interchange circuits used for transmission in opposite directions, the r
16、atio, expressed in decibels, of the voltage transmitted on one interchange circuit to the resulting voltage (cross-talk) at the receive end of the other interchange circuit. 3.5 cross-talk loss (far end): For two interchange circuits used for transmission in the same direction, the ratio, expressed
17、in decibels, of the voltage transmitted on one interchange circuit to the resulting voltage (cross-talk) at the receive end on the other interchange circuit. 3.7 environmental conditions: Those charac- teristics of the electrical or physical environment, for example EMI, ground potential difference
18、magnetic fields, altitude, temperature, etc., which may affect the operation, with respect to interchange circuits, of a DTE or DCE. 3.8 galvanic isolation: The existence of a element that is non-conductive with respect to the conductivity of common mode voltage, between the equipment containing a g
19、enerator and the equipment containing a receiver of an interchange circuit. 3.9 generator: The component of an interchange circuit that is the source of the transmitted signal. NOTE - The term generator is used interchangeably with the term driver. 3.10 generator offset voltage: The d.c. component o
20、f half the vector sum of the voltages between each conductor of a balanced interchange circuit generator and its signal ground reference NOTE - The d.c. component of half the vector sum of the voltages is the same as the arithmetic mean of the d.c. voltages in the above. 3.11 ground signal: The gene
21、rator/receiver signal voltage reference. 3.12 ground earth: The voltage reference established by conductive components having a conductive path to earth in the vicinity of the equipment including the generator/receiver. NOTE - Earth ground is generally synonymous with, and the same as, frame or buil
22、ding ground or protective ground. 3.13 ground potential difference: The difference between the signal ground potentials of the generator and the receiver of an interchange circuit. The potential is the same as the difference in the earth ground potential difference only if the signal ground is conne
23、cted to earth ground at both the generator and the receiver. 2 ISO/IEC 8482:1993(E) 3.14 induced noise: An interfering voltage that is in- troduced into an interchange circuit by electromagnetic induction from currents in other conductors. For balanced interchange circuits induced voltages generally
24、 appear in the common mode. 3.15 interchange circuit: The circuit, including a generator, a receiver and interconnecting media, that provides for the interchange of signals across an interface, for example DTE/DTE, DTUDCE, DCE/DCE. 3.16 interchange point: The point in an interchange circuit at which
25、 the specified electrical characteristics of the circuit apply and should be measured. NOTE - The interchange point usually defines the line of demarcation between- equipment and is location of an interface connector. 3.17 receiver: The component of an circuit that provides for the detection of circ
26、uit signals at the receiving equipment. usually the interchange interchange 3.18 rise time: The time required for a generator output signal voltage to change from a value characteristic of one state to a value characteristic of a second state. It is most often specified as the time for the signal vo
27、ltage to pass between the 10 % and 90 % points of the wave form. NOTES 1 Rise time is normally dependent on the load and is usually specified for a specific test termination. 2 For unbalanced generators, the time for the change from an ON or active state to an OFF or inactive state is sometimes refe
28、rred to as the “fall time”. 3.19 site conditions: The environmental conditions for a given site. 3.20 surge voltage resistance: The ability of an interchange circuit to function normally after being subjected to surges having peak voltages up to some specified value. NOTE - Surge voltage resistance
29、is sometimes referred to as surge immunity. 3.21 surge voltage: A transient voltage wave appearing on an interchange circuit as a result of induction or other phenomenon and having a relatively high value and short duration. It is normally acceptable for such surges to cause errors or malfunctions.
30、NOTE - Surges are normally specified with the intent of assuring that equipment will not be damaged by such unusual conditions. 3.22 unbalanced interchange circuit: An interchange circuit that uses one conductor together with a second return conductor, normally signal ground, which is used in common
31、 by several circuits. 4 Symbolic representation of an in- terchange circuit (see figure 1) The symbolic representation of an interchange circuit is in principle as given in ITU-T Recommendation v.ll. However, the generator specified in this International Standard includes an additional control to pl
32、ace the device into the active state or the inactive, high impedance zero voltage state. This addition is shown in the symbolic representation reproduced in figure 1. 3 ISO/IEC 8482:1993(E) Generator High impedance control -7 -i Balanced I interconnecting cable I Receiver I Generator Receiver interc
33、hange point interchange point V ab = Generator output voltage between points A and B V ac = Generator voltage between points A and C bc = Generator voltage between points B and C Vs = Ground potential difference 4 = Cable termination resistor A, B and A, B = Interchange points c, C = Zero volt refer
34、ence interchange points (Signal ground) NOTES 1 Two interchange points are shown. The output characteristics of the generator, excluding any interconnecting cable, are defined at the “generator interchange point”. The electrical characteristics to which the receiver must respond are defined without
35、the cable termination resistor at the “receiver interchange point”. 2 Points C and C may be interconnected and further connected to protective ground if required by national regulations. Figure 1 - Symbolic representation of interchange circuit 5 Interconnection configurations (see figures 2 and 3)
36、In general, the interconnection configuration consists of one balanced trunk cable, which may be up to 1 200 m in length, and several balanced branch cables, each connecting an individual endpoint system to the common trunk cable. The branch cable connection points may be spaced as appropriate. A br
37、anch cable should be kept as short as possible and in any case not exceed 1 m in length. The balanced trunk cable shall be terminated by a termination resistor at each end. This facilitates the generator/receiver load measurements defined in 6.1.2. For connection of the endpoint systems to the trunk
38、 cable, a branch/trunk cable connector should be used. The connector(s) at each end of the trunk cable shall accommodate the termination resistor(s). Balanced cables may be shielded if required by local regulations. It may also be necessary to extend shielding across the branch/trunk cable connector
39、s. Depending on the type of multipoint operation, either a two wire or a four wire interconnection configuration may be used. For example, figure 2 shows a two wire multipoint configuration for half duplex data transmission, while figure 3 shows a four wire multipoint configuration for either half d
40、uplex or duplex data transmission. Balanced two-wire trunk cable /-1 -t- -+- Rt I _ $-t- 1) I - I I I Rt I -wire j- - -, f-1 I -t- - -/ & 2) Endpoint system Endpoint system Endpoint system Figure 2 - Two-wire multipoint configuration Balanced four-wire trunk cable 4 Rt Rt Rt Endpoint system Endpoint
41、 system Endpoint system Legend : 1 Signal ground & Protective ground NOTES 1) Interconnection of the endpoint system signal ground is optional and depends on local regulations. 2) Branch cable shield is optional and, when provided, it connects to the endpoint system protective ground, which may be f
42、urther connected to the signal ground. 3) Trunk cable shield is optional and, when provided, it connects to a protective ground at one place. Interconnection of shield to branch cable shields may be necessary. Figure 3 - Four-wire multipoint configuration 5 ISO/IEC 8482 1993(E) 6 Load on the multipo
43、int medium Each endpoint system represents a load to the multipoint medium. The load consists of a passive generator and/or a receiver with associated internal wiring and a balanced branch cable as shown in figures 2 and 3. In accordance with the multipoint half duplex data transmission principle, o
44、nly one generator is in the active state at a given time. Successful operation requires specification of the load in terms of dc. loading and a.c. loading. For d.c. loading, the component specification in clauses 8 and 9 are selected such that an active generator can drive the interconnecting trunk
45、cable, terminated at each end with not less than 120 Q, and 32 so-called Unit Loads (ULs), representing the total load of all endpoint systems. The value of 1 ,O UL is defined in 6.1.1. 6.1 Specification of d.c. loading The d.c. loading specification limits the current of an active generator to a pr
46、actical value. For this reason, a hypothetical Unit Load (UL) is defined for a current/voltage measurement. 6.1.1 UL definition (see figure 4) The value of 1,0 UL is defined by a current ranging between - 0,8 mA and + 1,0 mA when varying the voltage between - 7 V and + 12 V. The correspondent curren
47、t/voltage diagram is shown in figure 4. The voltage range takes into account the output and offset voltage of the generator, the common mode and internal voltage of the receiver and the power supply voltage. 6.1.2 UL determination of the endpoint systems (see figures 5 and 6) When measuring the curr
48、ent/voltage characteristics at the disconnected branch/trunk cable connector of one endpoint system, the measured generator shall be in the inactive state. The measurement configuration is shown in figure 5. The current/voltage measurement corresponds to that of the V.11 receiver input in ITU-T Reco
49、mmendation V.ll, i.e. with the voltage Ya (or vb) ranging between - 7 V and + 12 V, while yb (or lia) is held at zero volts, the rC?SUhing input current /ia (or /ib) should remain within the shaded range shown in figure 4. These measurements apply with the power supply of the generator and/or receiver in both the power-on and power-off conditions. To determine UL from the measurements, the slope of the bounds of the current limit of one UL, see figure 4, shall be modified to the minimum slope required to fully contain the current/voltage characteristics,
