1、 TIA-485-A-1998 APPROVED: MARCH 3, 1998 REAFFIRMED: MARCH 28, 2003 REAFFIRMED: DECEMBER 7, 2012 TIA-485-A (Revision of TIA-485) March 1998Electrical Characteristics of Generators and Receivers for Use in Balanced Digital Multipoint Systems NOTICE TIA Engineering Standards and Publications are design
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19、SE OF THE CONTENTS HEREOF, AND THESE CONTENTS WOULD NOT BE PUBLISHED BY TIA WITHOUT SUCH LIMITATIONS. ANSI/TIA/EIA-485-A i ELECTRICAL CHARACTERISTICS OF GENERATORS AND RECEIVERS FOR USE IN BALANCED DIGITAL MULTIPOINT SYSTEMS (From TIA/EIA Standards Proposal No. 3498 formulated under the cognizance o
20、f TIA Subcommittee TR-30.2 on Data Transmission Interfaces) CONTENTS Page 1 SCOPE 1 2 DEFINITIONS, SYMBOLS AND ABBREVIATIONS. 1 3 APPLICABILITY 2 4 ELECTRICAL CHARACTERISTICS 3 4.1 Unit load characteristics 5 4.1.1 dc Unit load specification 5 4.1.2 ac Load characteristics 6 4.2 Generator characteri
21、stics 7 4.2.1 Open circuit output voltages . 7 4.2.2 Differential and offset output voltages 7 4.2.3 Differential output voltages with common-mode loading . 8 4.2.4 Off-state output current 9 4.2.5 Short-circuit output characteristics . 9 4.2.6 Transient over voltage tolerance 10 4.2.7 Output signal
22、 waveform 10 4.3 Receiver characteristics 10 4.3.1 Input voltage ranges . 12 4.3.2 Input thresholds 12 4.3.3 Input balance measurements . 12 4.3.4 Receiver unit load test 13 4.3.5 Transient over voltage tolerance 13 4.4 Transceiver characteristics . 13 4.5 System requirements 13 4.5.1 Balanced inter
23、connecting media characteristics . 13 4.5.2 Cable termination . 14 4.5.3 Total load limit 14 4.5.4 Fail-safe operation . 14 Annex A (informative) 15 ANSI/TIA/EIA-485-A ii A.1 Multipoint system configuration . 15 A.2 Data signaling rate vs. cable length 15 A.3 Stub lengths 15 A.4 Optional grounding a
24、rrangements. . 15 A.4.1 Signal common (Ground) . 15 A.4.2 Configuration “A” 15 A.4.3 Configuration “B” 16 A.4.4 Shield ground . 16 A.5 References . 16 ANSI/TIA/EIA-485-A iii FOREWORD (This foreword is not part of this Standard.) This Standard was formulated under the cognizance of TIA Subcommittee T
25、R-30.2 on Data Transmission Interfaces. This Standard specifies generators and receivers capable of operating in balanced digital multipoint systems. The parameter values specified in this Standard are similar to those in TIA/EIA-422-B. These values allow generators and receivers to be designed that
26、 can be used to meet the requirements of both standards. No technical changes have been incorporated into TIA/EIA-485-A which will create compatibility problems with equipment conforming to previous versions of this Standard (EIA RS-485). The Telecommunications Systems Bulletin TSB-89 contains appli
27、cation guidelines on TIA/EIA-485-A. Topics covered include: data signaling rate vs. cable length, stub length, configurations, and other important considerations. This Standard is compatible with ISO/IEC 8482:1993 Information Technology - Telecommunications and information exchange between systems -
28、 Twisted pair multipoint interconnections. Annex A of this Standard is informative and provides a minimum set of guidelines for application, and is not considered part of this Standard. ANSI/TIA/EIA-485-A iv BLANK PAGE ANSI/TIA/EIA-485-A 1 1 SCOPE This Standard specifies the electrical characteristi
29、cs of generators and receivers that may be employed when specified for the interchange of binary signals in multipoint interconnection of digital equipment. When implemented within the guidelines of this Standard, multiple generators and receivers may be attached to a common interconnecting cable. A
30、n interchange system includes one or more generators connected by a balanced interconnecting cable to one or more receivers and terminating resistors. The electrical characteristics of the circuit are specified in terms of the required voltage, current, and resistance values obtained by measurements
31、 at the equipment interconnect points. This Standard does not specify other characteristics, such as signal quality, timing, protocol, pin assignments, power supply voltage, operating temperature range, etc., that are essential for proper operation of interconnected equipment. Any devices complying
32、with this Standard shall do so within the ranges of those factors appropriate for the device operation, such as power supply voltages, and ambient temperature. It is intended that this Standard be referenced by other standards and specifications that specify the additional characteristics necessary
33、to assure satisfactory interoperation of equipment. This Standard is compatible with ISO/IEC 8482:1993 Information Technology - Telecommunications and information exchange between systems - Twisted pair multipoint interconnections. 2 DEFINITIONS, SYMBOLS AND ABBREVIATIONS For the purposes of this St
34、andard, the following definitions, symbols and abbreviations apply: 2.1 Common-mode voltage (Vcm), one half of the sum of the voltages between each conductor of a balanced interchange circuit and ground. The common-mode voltage is the sum of ground potential difference, generator offset voltage and
35、longitudinally coupled noise voltage. 2.2 Data signaling rate, expressed in the units bit/s (bits per second), is defined as 1/T where T is the minimum interval between two significant instants. 2.3 Differential, the signal is the voltage difference between the A and B, not with respect to common (C
36、). 2.4 Generator (Driver), the component of an interchange circuit that is a source of the transmitted signal. 2.5 Ground potential difference (Vgpd), the difference between the signal ground potential between the active generator and a receiver of an interchange circuit. 2.6 Longitudinally coupled
37、noise voltage, unwanted voltage coupled inductively or capacitively between any two points along the balanced interconnecting cable (see 2.1). ANSI/TIA/EIA-485-A 2 2.7 Multipoint, a bus structure that has two or more generators and one or more receivers. 2.8 Off-state (Passive), the output state of
38、the generator when it is not in either of the two active states. In this state, the output presents a high impedance. 2.9 Receiver, the component of an interchange circuit that provides for the detection of interchange circuit signals at the receiving equipment. 2.10 Star (*), represents the complem
39、entary logical state of a binary signal. For example, the symbol Q represents the receiver output state for one input condition, while Q* represents the output state for the opposite input state. 2.11 Transceiver, a component that includes both a receiver and generator. 2.12 Measured parameter: Iib2
40、.13 Forced voltage: Via3 APPLICABILITY The provisions of this Standard apply only to the electrical characteristics of generators and receivers employed in communications between equipment. The information being conveyed is in the form of binary signals that may have a dc component. This Standard is
41、 not, therefore, an interface standard, but shall be referenced by those interface standards or specifications employing generators and receivers having these electrical characteristics. The circuits whose characteristics are specified herein will be utilized normally in data, timing, or control int
42、erconnections where the data signaling rate is up to 10 Mbit/s. Devices meeting the electrical characteristics of this Standard need not operate over the entire data signaling rate range specified nor be limited to 10 Mbps. They may be specified to operate at data rates to satisfy specific applicati
43、ons. The upper bound is application dependent and beyond the scope of this Standard. Maximum data signaling rate is typically limited by the following: ratio of signal transition time to the unit interval, maximum allowable stub length, and the bandwidth of the interconnecting media. The characteris
44、tics are defined such that any device in the system can operate with a common-mode voltage as great as 7 V. Compliant generators may be active simultaneously (contention) without damage. While generator contention may exist, there is no provision within this Standard for the detection of contention.
45、 ANSI/TIA/EIA-485-A 3 While the balanced generators and receivers described in this Standard are intended for use at high data signaling rates, they may (in preference to the unbalanced generators and receivers) generally be required where any of the following conditions prevail: a) A multipoint (mu
46、ltiple generator) system is required. b) The interconnecting cable is too long for effective unbalanced circuit operation. c) The interconnecting cable is exposed to extraneous noise sources that may cause an unwanted voltage up to 7 V measured differentially between the signal conductor and circuit
47、 common at the load end of the cable with a 50 resistor substituted for the generator. d) Logical inversion of the signals may be required. 4 ELECTRICAL CHARACTERISTICS Figure 1 shows an interconnection application of generators and receivers having the electrical parameters specified in this Standa
48、rd. The elements in the application are: - Generators - Receivers - Transceivers - Balanced interconnecting cable - Termination resistors (RT) The steady-state load on a single active generator shall be defined in the terms of unit loads (ULs). The load on the system caused by each receiver and pass
49、ive generator shall be specified by the number or fractions of unit loads each presents. A unit load is defined by the current-voltage characteristics specified in 4.1.1. A load is defined as a passive generator (G), a receiver (R), or both (a Transceiver (T). The electrical parameters specified in the following sections are selected so that a generator can drive a total load having the value of 32 unit loads and an effective total termination resistance as low as 60 while providing a minimum differential voltage of 1.5 V. ANSI/TIA/EIA-485-A 4 RT RTGRGRABCABCA/A
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